XIEKE of the week

Buckvballs Can Come from Outer Space J

Carbon-rich meteorites that crash to Earth carry a wealth of information from far-flung regions of outer space. Now, it seems that some extraterrestri- al baggage survives the long journey intact. A new study shows that carbon molecules known as fullerenes can originate outside the solar system and ride in on meteors.

Fullerenes are hollow, spherical mole cules made of pure carbon (SN: 6/27/98, p. 406). The most famous member of the family is buckminsterfullerene, consisting of 60 carbon atoms arranged in the pattern of a soccer ball. On Earth, fullerenes can be made in the lab and have been found in rocks seared by lightning strikes.

Luann Becker of the University of Hawaii in Honolulu and her group isolated fullerenes from the Allende and Murchison meteorites. Both are carbonaceous chon- drites, a rare meteorite type that contains much organic material. The researchers found, trapped inside the fullerenes, noble gases whose isotopic profile did not match those of gases on Earth.

The researchers also isolated fullerenes from a clay sediment layer deposited dur- ing an asteroid impact 65 million years ago. Some scientists believe that this colli- sion, marking the so-called Cretaceous- Tertiary (KT) boundary, led to the demise of the dinosaurs (SN: 3/1/97, p. S20). The sediment fullerenes also contain noble gases with unusual isotope ratios.

This research lends support to the idea that organic molecules from space could have played a role in starting the chemical processes necessary for the origin of life (SN: 1/9/99, p. 24). “It confirms the possi- bility of organic compounds surviving the trauma of a large [meteor] impact,” says Jeffrey L. Bada of the University of Califor- nia, San Diego.

The findings of Becker, Robert J. Pore da of the University of Rochester (N.Y.), and Ted E. Bunch of NASA Ames Re- search Center in Moffett Field, Calif., ap- pear in the March 28 PROCEEDINGS OF THE

In 1996, Becker’s group discovered fullerenes in rocks from the Sudbury Im- pact Crater in Ontario. This crater was made by an asteroid that hit Earth 1.85 billion years ago. These fullerene mole- cules contained helium with isotope ra- tios that are “truly out of this world, al- most out of the solar system,” says Bada.

The 1996 work “came under thorough examination and scrutiny,” says Becker, because the fullerenes in the crater may have arrived intact from elsewhere in the universe or formed on Earth, perhaps during the asteroid’s fiery impact.

Last year, Becker and her colleagues

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4 buckyball with a trapped atom ofgas, perhaps b m outer space {let?). Breaking a bond opens i window {center], and the gas escapes (right).

for the first time found fullerenes within a meteorite.

More recently, the researchers ground up several grams of samples from two meteorites and the KT boundary sedi- ment. They extracted fullerenes and heat- ed them under vacuum to make “the gas [inside] pop out,” says Becker.

The ratio of two helium isotopes, heli- um-3 and helium-4, was higher in these fullerenes than in air. Most dramatic, in the Allende meteorite fullerenes, the ratio was

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several thousand times greater than in the atmosphere.

The high ratio confirms the fullerenes’ extraterrestrial origins. “If you get the unusual helium ratios, there’s no other way to explain it,” says Bada

“The helium got trapped at the time when the fullerenes formed and re- mained there for billions of years,” Becker explains. “These trapped gases can tell us about the early history of the universe.” The researchers extracted mostly car-

bon-60 and carbon-70, but the meteorites also contain an abundance of larger tullerenes, Becker notes. More difficult to extract, they may contain most of the trapped gases.

The results “strongly suggest that the tullerenes are extraterrestrial,” says Dieter Heymann, emeritus professor at Rice Uni- versity in Houston, who recently heard Becker lecture. However, it’s unclear when they formed, he adds. 4. wu

Researchers enjoy bitter taste of success Taste has been the most elusive of the

five senses. Now, genetic work is reveal- ing how taste buds handle the chemical information that washes over them.

Researchers have discovered a large family of tastecell proteins that seem to latch onto bitter chemicals, the first step in perceiving the flavor. The team also presents the first molecular genetic evi- dence for differences in taste perception, says Nicholas Ryba of the National Insti- tutes of Health in Bethesda, Md.

Scientists from NIH and the University of California, San Diego (UCSD) describe these findings in the March 17 CELL. The report comes soon after the first identifi- cation of a functioning taste receptor. It detects umami-the meaty flavor of monosodium glutamate and Parmesan cheese (SN: 1/29/00, p. 68).

The team looking for bitter-flavor recep tors had previously found two candidates (SN: 2/27/99, p. 132). However, those pro- teins weren’t made by the taste cells that produce the signaling protein, called gust- ducin, that’s known to be important for recognizing bitterness, says Ryba. So, he, Charles S. Zuker of UCSD, and their team had to look again for the bitter receptors.

Geneticists have known for a long time that some people can taste a bitter chemi- cal called 6n-propyl-2-thiouracil, or PROP, while others are oblivious to it (SN: 7/12/97, p. 24). When other researchers pinpointed a region of the human genome where the gene for PROP tasting lies, the NIH-UCSD group examined the area’s DNA

SCIENCE NEWS, VOL. 157

Bitter receptors (pen) are made by the same taste cells on a mtk tongue that make gustducin {red). Cells that make both types of protein appear yellow.

sequence. They found a gene there that en- codes a protein similar to receptors in the nose that recognize odors.

By searching human DNA databases, the group turned up 25 similar genes. Some of these had been linked to the taste of certain bitter compounds like quinine and cycloheximide. People may have 40 to 80 genes for bitter-recognizing proteins, Ryba estimates.

Fruit flies also have a family of taste-re- ceptor genes, Yale University researchers report in the March 10 SCIENCE.

Cells that make any of the newly found mammalian receptor proteins also pro- duce all the others and gustducin. How- ever, not all gustducin-producing cells

MARCH 25,2000