Question of the Month: How Do We Know That a Rock Found In the Ice In Antarctica Came From Mars?

Submitted by: Audra Martin, La Puente

Answered by: Bill Bottke, Postdoctoral Fellow, Division of Geological and Planetary Sciences

The short answer is that we do not know where the moon came from. It's difficult to know, because we have too few examples. Earth is the only terrestrial planet (that is, the only planet within the inner solar system, and made of rock as opposed to gas) that has a large satellite.How do we know that meteorites come from Mars?

Meteorites are rocks which fall to Earth from space. Most are thought to be fragments of asteroids which have survived fiery entry through Earth's atmosphere. Twelve of the thousand or so meteorites held in worldwide collections, however, are thought to come from Mars. Eleven of these meteorites, formed roughly 1.3 billion years ago, were named the SNC meteorites after the sites where they were found: "S"hergotty (India), "N"akhla (Egypt), and "C"hassigny (France).

The twelveth Martian meteorite is much older and different from the rest. It is called ALH 84001, named for the year it was discovered, 1984, and the location it was found, Allen Hills, Antarctica. It was formed 4.5 billion years ago, such that it was present when Mars had a much thicker atmosphere and liquid water on its surface. Recently, scientists have suggested that ALH 84001 might even contain fossil evidence for ancient Martian life.

How do we know that these meteorites are from Mars when people have never been there and no rocks have been collected on its surface? In 1976, two NASA spacecraft named Viking I and II landed on Mars and analyzed its atmosphere and surface. These spacecraft examined soil and air samples using on-board instruments, making careful measurements and radioing their data back to scientists on Earth. After careful study, it was determined that Mars' atmosphere was very different from Earth's atmosphere or any other combination of gases found in the solar system. Then, by analyzing small traces of gas trapped in the interior of these twelve meteorites, scientists were able to identify the characteristic "fingerprint" of the Martian atmosphere, proof that these rocks were blasted off Mars' surface at some time in the past.

Even before gas was discovered in these meteorites, scientists were suspicious that they might have originated on Mars. The SNC meteorites have young formation ages, and all twelve Martian meteorites have complex chemical compositions which set them apart from other known meteorites classes. Moreover, the abundance of oxygen isotopes (different kinds of oxygen) in the meteorites are inconsistent with oxygen isotopes found in Earth rocks.

However, the idea that makes most sense is that the moon arose from a giant impact during the formation of Earth about 4.5 billion years ago. While Earth was being formed, it was hit by very large objects, including bodies as large as Mars (about one-tenth the mass of Earth). If you had hit the growing Earth with such a body, material would have splashed out from the impact site, and a sizable amount of that would have gone into Earth orbit. This material may have come partly from the impacting body and partly from Earth itself. We think that this material could have then aggregated rather quickly into the moon as we know it.

According to this view of the origin of the moon, you would therefore have created a body that started out close to Earth (much, much closer than the present distance between Earth and the moon). This body would have been very hot, probably molten, because of the intense energy created in the impact, and it would have been a body with a composition similar to the outer parts of Earth, not Earth as a whole. The central part of Earth is an iron core; Earth as a whole has a lot of iron but the outer parts of Earth do not.

All of these characteristics are in agreement with the moon as we see it. The moon is moving away from Earth steadily and was therefore once much closer to Earth; it moves away because the tides that are raised by the moon in the oceans of Earth cause angular momentum to be transferred from the spin of Earth to the orbital motion of the moon.

In addition, we know from looking at lunar rock that the moon was once very hot, perhaps completely molten. When you look at the moon in the night sky or through a telescope, you see dark-colored regions and bright-colored regions; the bright-colored regions, called lunar highlands, are composed of very ancient rocks that arose through crystallization from molten rock, and this fits in with the idea of a very traumatic beginning.

The moon also has very little if any metallic iron; it does not have a significant core. This fits in with the idea that the moon is derived >from material that was in the outermost parts of the early Earth or of the projectile, most likely both. The absence of a core in the moon is otherwise very difficult to explain-- it's one of the main reasons we do not think that the moon formed somewhere else in the solar system and then got captured, since if it had formed somewhere else it would be very difficult to understand why it has this composition.

Perhaps the main reason why this idea of a giant impact is attractive is that the angular momentum of Earth and moon together is about what you would get from such an impact. It turns out that this amount of angular momentum, which was once in the spin of Earth and is now mostly in the orbital motion of the moon, is about what you would get if an object approximately the mass of Mars hit Earth (obliquely, not head on). So all of these things fit in together.

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Robert Tindol
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New Diagnostic Test Announced for Group of Brain Diseases

PASADENA— Scientists have developed a simple diagnostic test for transmissible spongiform encephalopathies (TSEs), a group of invariably fatal brain diseases that include "Mad Cow" disease in cattle and Creutzfeldt-Jakob disease (CJD) and kuru in humans.

According to Dr. Michael Harrington of the California Institute of Technology, he and his colleagues at the National Institute of Neurological Disorders and Stroke have developed the test by identifying a diagnostic protein found in the spinal fluid of infected humans and animals. Their research appears today in the New England Journal of Medicine.

Harrington, a scientist at Caltech's Beckman Institute, says that the test is an important contribution to public health because it can help prevent future transmissions of the diseases. "This should reduce the risk of accidental transmission, allow better patient management, and could even provide an objective measure for any future treatment," Harrington says.

Dr. Kelvin Lee, Harrington's colleague at Caltech, adds that the test should be of considerable interest in Great Britain. In the last year, a form of the disease known as bovine spongiform encephalopathy (also known as BSE, or "Mad Cow" disease) has been linked to a new strain of CJD, which has affected several individuals in Britain.

"This test potentially enables us to screen cattle and herds for BSE and thus reduce the possibility that BSE-contaminated beef could enter the food chain," Lee says. "Moreover, it will provide a means for selectively destroying BSE cattle as opposed to unaffected cattle, and make the international exchange of animals more safe."

TSEs are degenerative diseases of the nervous system characterized by rapidly progressive dementia and uncontrolled limb spasms in both humans and animals. The diseases are always fatal, and postmortem examinations reveal spongelike holes in the brain.

The causitive agent of these transmissible diseases is believed to be a prion, an infectious protein that accumulates in the brain and results in neuronal destruction. Prions have been shown to be particularly resistant to standard decontamination procedures.

Diagnosis of these disorders has relied on brain biopsy or postmortem examination for the presence of the prion. In work published by Harrington in 1986, he showed that a particular protein was present in the cerebrospinal fluid of patients affected with CJD and could serve as a useful molecular marker for this disease.

The new findings identify that protein as 14-3-3, a normal neuronal protein. "We hypothesize that 14-3-3, which is normally present in neurons, leaks into the spinal fluid as a result of the neuronal destruction that occurs in TSEs," says Harrington. The identification of the protein as 14-3-3 has enabled the development of a simpler test for the diseases.

Also involved in the study are Drs. Clarence J. Gibbs, Jr., Kimbra Kenney and Gary Hsich, all of the National Institutes of Health's National Institute of Neurological Disorders and Stroke.

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Robert Tindol
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New Research Shows How the Eyes Help the Body Navigate

PASADENA— Neuroscientists have new results on how our brains and eyes work together in getting our bodies from point A to point B without mishap. The research appears in today's issue of the journal Science.

According to Dr. Richard Andersen, James G. Boswell Professor of Neuroscience at the California Institute of Technology, the research shows how different parts of the brain work together to allow for navigation. When a driver is speeding down the interstate and looking at exit signs, for example, he can competently remain traveling in a straight line because of the way his brain is wired. The study in Science reveals more about the precise nature of this wiring.

Andersen's studies of neural impulses in the brain show that humans and animals see things literally in a straightforward way if they are moving and looking directly ahead. When the movement is simple, a fingernail-size area located within the cortex of each hemisphere of the brain an inch or two above each ear interprets the data from the eyes and allows the body to navigate forward. This region is known as the dorso-medial superior temporal area (MSTd), and is sufficient to compute the direction of self-motion as long as the eyes and body are both pointed directly ahead.

But when it becomes necessary or convenient to look around while the body is traveling forward, things get a bit more complicated in the brain. Andersen's research shows that the MSTd area still likes to interpret motion with the same visual neurons at work, but that additional information must come from another part of the brain to help process the more complicated information.

"When the eyes move, the images on the eyes shift as a result of the eye movements," says Andersen. "The brain knows that it's moving its eyes, so a signal about the eye movement is sent to MSTd."

The eye-movement information is then combined with the incoming visual signals to allow for reliable navigation to take place. The process is automatic, and presumably evolved so that humans and animals could walk forward while glancing to the side, Andersen adds.

"We know that the brain has no problem in doing this, just from the fact that people don't drive off the road when they look around," says Andersen.

Though the Science article reveals much about how the brain combines images and motor signals to allow for navigation, Andersen says that additional research should reveal more about the precise mechanism.

For example, the researchers are not yet sure whether motor areas of the brain that are responsible for moving the eyes are indeed projecting the signals back into this sensory area. Another possibility is that sensors in the eye muscles themselves tell the brain what the eyes are doing when they glance about. Also, the researchers would like to find out precisely how the mechanism works when the head rotates but the eyes do not move at all. Again, from everyday experience, humans are able to glance about either by moving the eyes or moving the entire head while moving in another direction, and one would suspect that head movements are also accounted for during navigation. Nonetheless, there are situations in which the eyes can play tricks on the brain, Andersen says. And this research could have several applications in the future for helping humans orient themselves. For example, the knowledge gained could help in the design of better flight instruments for pilots in cases where visual information is misleading.

Also, the research could lead to more realistic flight and driving simulations. And at a more basic level, the research is already providing new insights into the nature of vision and the brain. "The experiments will help us to understand how we perceive and act within the world around us," says Andersen.

The research was funded by the National Eye Institute, the Sloan Center for Theoretical Neurobiology at Caltech, the Office of Naval Research, and the Human Frontier's Scientific Program. Other authors of the paper were David C. Bradley, Marsha Maxwell, and Krishna V. Shenoy, all of Caltech; and Martin S. Banks of the University of California at Berkeley.

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Robert Tindol
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Question of the month: Why do magnets stick to other magnets?

Question of the Month Question from: Matthew, age 8 1/2, Pasadena

Answered by: Doug Michael, PhD, Senior Research Fellow in Physics

Magnets stick together because they have a magnetic field around them, and this field both pulls on and pushes away other magnets.

If you've played with magnets like those that stick to your refrigerator, you know that sometimes they stick to each other, but that they also can push each other away, depending on which way the magnets are pointing.

Each magnet has a north pole and a south pole (named after the earth's magnetic north and south poles), and the north end of one magnet will stick to the south end of another magnet. But if two north poles or two south poles are placed near each other, the magnets will push each other away.

But this explanation doesn't really say HOW magnets pull and push on each other. To answer that question, we need to think about what creates a magnetic field.

Magnets like those on your refrigerator, which always have a magnetic field, are called permanent magnets. The secret of permanent magnets lies in the material they're made of, which usually is metal that contains a lot of iron.

All matter is made of atoms, which contain electrons. And electrons act like miniature magnets. This is a basic trait of electrons, which arises from physical laws.

In most materials the tiny magnetic fields of electrons point in all different directions, so they neutralize each other and there is no large magnetic field. But in iron and a few other metals that are used to make permanent magnets, these countless tiny magnets are pointing in roughly the same direction. Each miniature magnetic field adds to and reinforces all the others. The total effect creates a noticeable magnetic field, which will pull and push on other, nearby magnets.

Another way to create a magnetic field is with moving electric charges. Electric charges that are standing still exert constant electric forces on the objects around them. But electric charges that are moving exert changing electric forces on the objects around them. If the changing electric forces are all added up as the charges go by, the result is a magnetic field.

Moving electric charges create a magnetic field no matter how they are moving: in a straight line, a spiral, a circle, or some unusual path. One way to create a fairly strong magnet is by sending electricity through a coil of wire; this is called an electromagnet. Electromagnets are temporary magnets; the magnetic field goes away when the electricity is turned off.

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Question of the month: Why is there so much gravel in the San Gabriel Valley, especially around Irwindale?

Question of the Month Answered by: Lee Silver, W. M. Keck Foundation Professor for Resource Geology

The San Gabriel Valley contains huge amounts of gravel because the San Gabriel River carries broken rock out of the nearby San Gabriel Mountains. The San Gabriels produce especially large amounts of gravel for several reasons.

For one thing, they are very steep. The San Gabriel River leaves the mountains at the Santa Fe Dam, where the elevation is roughly 1,000 feet. Within just a few miles of this spot the river reaches mountains in the 7,000- to 10,000-foot range. This steepness, or "gradient" as geologists call it, affects how much mud, gravel, and rock a river is able to carry. The higher the gradient (the steeper the slope), the more material a river can transport.

The reason the gravel accumulates mainly in Irwindale is that the gradient decreases suddenly—that is, the river flattens out—right there. The river can carry lots of debris as long as its course is steep, but as soon as the river leaves the mountains and its channel levels out, most of the debris settles out. Rock and gravel have been accumulating in the San Gabriel Valley for hundreds of thousands of years and is probably thousands of feet deep in the Irwindale area.

Another factor that helps the San Gabriels produce more gravel than most other mountains is the ongoing earth movement we have in Southern California, which we sometimes feel as earthquakes. When the earth moves in a large earthquake, the mountains often grow a few inches, and sometimes gain several feet. So even though erosion is constantly wearing down mountains everywhere, the San Gabriels are better able to maintain their height, steepness, and ability to produce lots of gravel.

Also, because Southern California sits astride a boundary between tectonic plates, the rock in the San Gabriels tends to be highly fractured. This makes it treacherous for climbing, and means that it breaks into chunks more easily than solid, unfractured rock.

Because of their height, the mountains can create their own weather, and actually draw moisture out of passing clouds. The high elevations get many times more rainfall than the flatlands just a few miles away. This heavy rainfall collects in the steep streams and rivers and forcibly sweeps the gravel out into the valley.

The location of the many gravel quarries in Irwindale is a historical accident. Homeowners didn't want to live on the San Gabriel River floodplain because of the risk of flooding. So the gravel companies moved in instead, established mineral rights to the land, and started mining gravel. The gravel is used as an aggregate material in concrete, and is one of the Los Angeles region's most valuable mineral products.

Besides gravel, the San Gabriel River also carries a lot of water out of the mountains. Much of the water is left to stand in settling basins, which can be seen to the west of the 605 Freeway. They may look like flooded gravel quarries, but actually the water is left there on purpose, so that it can soak into the ground and replenish the underground water table.

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Question of the Month: How does an MRI work, and why is it so noisy?

Question of the Month Answered by: Russ Jacobs, Ph.D., Member of the Beckman Institute, Biology

Magnetic resonance imaging machines, or MRIs, use strong magnetic fields and radio waves to look inside a patient without the need for surgery or the use of damaging radiation such as X-rays. MRIs have become standard equipment in many hospitals over the last decade.

When an MRI machine looks inside the body, what it really sees are water molecules. Because all parts of the body contain some water, MRIs can examine any part of a patient's body. Water molecules consist of oxygen and hydrogen atoms, and the core of a hydrogen atom—its nucleus—is a single proton.

These protons have a basic, inherent property called nuclear spin. One way to think about this nuclear spin is that the protons actually spin like a gyroscope or a top. Because the protons also have an electrical charge, the spin makes them act like tiny magnets.

Scientists have found that a magnetic field will make the spinning protons wobble, just like a spinning top that isn't quite vertical will wobble. And the stronger the magnetic field, the faster the wobble. But while a top might wobble around a few times in a second, nuclei wobble about 50 million times per second.

Scientists also know that if a proton is excited—that is, given some extra energy—by a radio wave, it will send that energy back out as a radio signal that is faintly detectable. The frequency of the proton's radio wave is determined by its wobbling rate; so the protons in water emit a radio frequency of about 50 million cycles per second.

The heart of an MRI is basically just a strong magnet and a radio transmitter and receiver, plus a lot of electronics to coordinate their operation. The magnet creates a strong magnetic field, hundreds of thousands of times stronger than the earth's magnetic field; the radio transmitter beams an intense burst of radio waves into the patient to excite the wobbling protons; and the receiver detects the protons' faint radio signal.

To create an image, MRIs must determine which radio signals are coming from which protons and plot these protons in their proper locations. To distinguish protons from one another, MRIs manipulate both the magnetic field and the burst of radio energy so that protons in different parts of the patient emit slightly different radio signals. The MRI detects these different signals, figures out automatically where they came from, and builds up a three-dimensional image.

MRIs also notice the strength of these radio signals. Where there is a lot of water, for example in muscle, the signal is strong, and where there is less water, for example in bone, the signal is weak. The different strengths of the radio waves enable the MRI to fill in the image with the proper shades of gray.

An MRI is noisy because its magnetic field is created by running electrical current through a coiled wire—an electromagnet. When the current is switched on, there is an outward force all along the coil. And because the magnetic field is so strong, the force on the coil is very large.

When the current is switched on, the force on the coil goes from zero to huge in just milliseconds, causing the coil to expand slightly, which makes a loud "click." When the MRI is making an image, the current is switched on and off rapidly. The result is a rapid-fire clicking noise, which is amplified by the enclosed space in which the patient lies.

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Keck II Telescope to Be Dedicated

PASADENA—The 10-meter Keck II Telescope will be dedicated in a mountaintop ceremony at 11:00 a.m. (Hawaiian Time) on Wednesday, May 8. Keck II and its five-year-old twin Keck I are the world's largest optical telescopes.

Edward C. Stone, director of NASA's Jet Propulsion Laboratory and chair of the board of directors of the California Association for Research in Astronomy (CARA), which owns and operates the telescopes, will lead the ceremony inside the Keck II dome on the summit of Mauna Kea, a 13,796-foot dormant volcano on the Big Island of Hawaii.

Following a traditional dedication chant by Hawaiian elder Kepa Maly, the audience will hear brief remarks from University of Hawaii President Kenneth P. Mortimer, California Institute of Technology President Thomas E. Everhart, University of California President Richard C. Atkinson, NASA chief scientist France Córdova, and Keck Foundation chairman and president Robert A. Day.

Clair W. Bergener, chair of the University of California Regents, and Gordon E. Moore, chair of the California Institute of Technology's Board of Trustees, will then make a joint presentation to Howard B. Keck, who served as the W. M. Keck Foundation's chairman and president for more than 30 years. The Keck Foundation has provided more than $150 million toward funding the telescopes.

As a finale, Stone will take the telescope for a spin, briefly demonstrating how the telescope and dome move. Although it weighs nearly 300 tons, the telescope is so precisely balanced that, with the brakes released, a person could move it by pushing with one hand. Keck II is presently operational for engineering tests and has taken a few astronomical images; it will be fully operational for science in October.

The Keck II Telescope, like its sibling Keck I, uses a mirror composed of 36 hexagonal pieces of glass, individually polished and assembled to form a perfectly parabolic reflecting surface with an effective diameter of 10 meters, or nearly 33 feet. This segmented mirror is much thinner, and therefore lighter in weight, than a solid mirror could be, which is the key to building such a large instrument.

In addition to doubling the amount of observing time available at the Keck Observatory, Keck II will allow a wider array of observing instruments to be used. Scientists have designed and are building three specialized spectrographs—instruments for recording an object's spectrum—for use on Keck II that will make possible an observational program with great flexibility and range.

The Near-Infrared Spectrograph will be able to record spectra from extremely faint objects at wavelengths just slightly longer than are visible to the human eye. DEIMOS, a powerful multi-object spectrograph, will be able to record spectra from up to 100 objects simultaneously. And the Echelle Spectrograph and Imager will have the ability to record a spectrum over an extremely broad range of wavelengths. These, together with the instruments of Keck I, are arguably the finest astronomical instruments in the world. Together, they allow each astronomer to customize his or her observations to suit the astronomer's individual needs.

Keck II will also have an adaptive optics facility that will enable it to produce images with a resolution of 0.04 arc seconds at a wavelength of 2 microns. Adaptive optics is a method of compensating for the slight distortions caused by atmospheric turbulence. People see distorted starlight as twinkling, but for a telescope making a long exposure, turbulence makes the star look slightly blurry. The adaptive optics system will be able to detect these atmospheric distortions and make one hundred tiny adjustments to the mirror per second to compensate for them and maintain the sharpest possible image.

In the long term, Keck I and Keck II have the potential to work together as an interferometer—a system in which light from one telescope is combined and interferes with light from the other telescope. Scientists can extract extremely high-resolution images from this interference. Because Keck I and Keck II are some 85 meters (nearly 280 feet) apart, they would have a resolution equivalent to a telescope with an 85-meter mirror, or about 0.005 arc seconds at a wavelength of 2 microns.

SATELLITE BROADCAST: Feed Date: May 8, 1996 Feed Time: 10:45 a.m. to 12:15 p.m. Hawaiian Time 4:45 p.m. to 6:15 p.m. Eastern Time Coordinates: Satellite Galaxy K4, Transponder 11, Channel 51 Downlink frequency 11915 MHz V

IMAGES AVAILABLE: Three of the first space images taken with the Keck II Telescope are available through Andy Perala at the Keck Observatory, through Reuters, Agence Presse France, and UPI, and, for AP Photo Members only, through Photostream.

Captioned photos of the twin Keck Telescopes are available from the above sources, and from Jay Aller and Max Benavidez at Caltech.

Question of the month: What exactly is mad cow disease?

Question of the Month Answered by: Michael Harrington, Member of the Beckman Institute at Caltech in biology

Formally called bovine spongiform encephalopathy—or BSE for short—mad cow disease is the common name of a fatal illness that many cattle in the United Kingdom have. Bovine means related to cattle; encephalopathy has Greek roots and means brain disease; and spongiform means literally "in the form of a sponge." Put it all together, and BSE is a disease of cattle in which the brain ends up looking like a sponge, full of holes.

The term mad cow disease comes from the strange behavior and odd staggering gait of affected cattle. The sick animal loses its sense of balance and lurches or stumbles around in circles, making it appear crazy.

BSE is closely related to a centuries-old disease in sheep called scrapie, and to some human diseases, notably an illness called Creutzfeldt-Jakob disease, or CJD for short. Scientists believe the disease is spread when one animal eats infected tissue from another animal. In fact, scientists believe the current epidemic among British cattle was caused by using the processed offal of scrapie-infected sheep as a supplement in cattle feed. While the disease can occasionally move between species, the source for CJD in humans is not known, except for a small number of families in which it is genetic.

Public-health experts in Britain have been aware of BSE since the mid-1980s, and have repeatedly assured the public there was no chance that humans could be infected by eating beef. Then in March, after looking at 10 new cases of Creutzfeldt-Jakob disease in which the patients were much younger than usual, they announced that it might be possible for humans to be infected by eating beef after all.

While scientists know that the disease can be spread between animals when animals eat infected tissue, scientists know few of the details. The infectious agent is not a bacteria or a virus, but a poorly understood type of protein called a prion. Prions were discovered in the 1980s, and no one knows yet how they result in disease.

More puzzling still, cooking contaminated beef doesn't inactivate the infectious agent, as it does with bacteria and parasites. Prions heated to a temperature that will destroy most proteins (130 degrees Celsius, or 266 degrees Fahrenheit), retain their ability to transmit the disease.

Although the British government stressed that there is only very weak and indirect evidence for a link between the illness in cattle and in humans, British beef sales plummeted. As more information has become available and beef prices have dropped over the last several weeks, Britons have resumed eating beef, but at slightly lower levels than before.

American agriculture and health experts believe this country is safe from BSE, because British beef imports to the United States have been banned since 1989 to protect U.S. cattle from infection. Also, American farmers don't use sheep products as a supplement in cattle feed.

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Chemical Engineers Show that Directed Evolution Can Be Useful

PASADENA—Caltech engineers have shown for the first time that an experimental technique known as directed evolution can solve real, industrial problems in pharmaceutical manufacturing.

The result, published in the April 1 issue of Nature Biotechnology, describes how the researchers used directed evolution to develop a new enzyme that is able to catalyze—increase the reaction rate of—an important step in the manufacture of an antibiotic.

"We're very excited to demonstrate that the technique works on a problem of real, industrial interest," said Frances Arnold, an associate professor of chemical engineering at Caltech. She collaborated on the research with Jeffrey C. Moore, a graduate student in chemical engineering.

The production of most chemicals, including antibiotics, requires many steps, some of which are quite slow. To speed up these steps, chemical engineers use catalysts, which can be metals, metal-based molecules, or ordinary enzymes.

In the present case, researchers were working on a step in the production of a class of antibiotics derived from cephalosporins. The pharmaceutical company Eli Lilly, while developing the manufacturing process for these antibiotics some years ago, found that zinc catalyzes this step effectively, but the zinc process is expensive, and they wanted to use something less costly.

Company scientists thought a naturally occurring enzyme might catalyze the reaction, in this case cutting molecules called p-nitrobenzyl esters into two smaller pieces, one of which forms the basis for an antibiotic called loracarbef. After screening many enzymes they finally found one that catalyzed the reaction, but it was only weakly effective, so they suspended research on the project.

In 1994 Eli Lilly gave the enzyme to Arnold, to see whether her lab might improve it using directed evolution. Directed evolution is a process in which the gene that produces a natural enzyme is mutated so that it produces variants of the enzyme. Several generations of mutation and screening for enhanced activity can significantly improve the enzyme.

Enzymes are made of strings of hundreds of amino acids, and the mutated genes typically create enzymes with several of the many amino acids replaced by different ones. Substituting amino acids can change the shape and function of the enzyme. Some variants are less effective, some are more so. Researchers take the new, variant enzymes and test them for the desired activity. The genes that produce the best, most active enzymes are saved and they are either further mutated or recombined, and the new variants are screened again for their effectiveness. At each step, scientists save the genes that produce the most active enzymes to become the "parents" for the subsequent generation.

To create an industrially useful catalyst, Moore and Arnold needed to increase the enzyme's activity by at least 10 times. They far surpassed their goal. After five generations of mutations, recombinations, and screenings, they found enzymes that are as much as 30 times more active than the one they started with.

As it turns out, the new enzymes won't be used commercially yet, because the pharmaceutical company had already received approval from the Food and Drug Administration to manufacture the antibiotic using the zinc catalyst. And though the zinc process is expensive, it would cost the company even more to go through the FDA approval process again.

But that's of little concern to Arnold. "Of course it would be nice if we had started work on this novel enzyme earlier, so that it could have been used commercially," Arnold said. "But it may be used for other products. And, more important, we've shown the capability of this technique to solve real problems. I'm sure it will find many useful applications in the future."

Contact: Jay Aller (818) 395-3631 aller@caltech.edu

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JA
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Question of the month: How long is a radio wave, and how do you measure it?

Question of the Month Answered by: Sterl Phinney, Associate Professor of Theoretical Astrophysics

Radio waves come in a variety of lengths, from as short as an inch or less up to several miles. The waves we usually think of as radio waves, the ones that broadcast music and weather reports, range in length from about 10 feet for FM to about 300 yards for AM stations.

Radio waves are electromagnetic radiation, just like x-rays at the dentist, gamma rays from space, the microwaves that cook your food, visible light that allows us to see, and infrared radiation that we feel as heat. The only difference between these kinds of radiation is their wavelength.

We can't measure radio wavelengths directly, like we can an ordinary object, because they are invisible and move at the speed of light. So we have to measure them in a clever, indirect manner.

The method is comparable to measuring the length of boxcars in a moving train. Because they are moving, we can't use a tape measure on a boxcar. But if we know the speed of the train and how often a boxcar goes by, we can figure it out. If the train is moving at 80 feet per second, and two boxcars go by in each second, then each car must be (80 ÷ 2 =) 40 feet long.

Similarly, radio waves move at the speed of light, about 300 million meters per second. For an FM station at 100.0 on your dial, 100.0 million wavelengths go by in each second. So the wavelength is (300 million ÷ 100 million =) 3 meters, or about 10 feet.

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