of the week

Rocks Mav Have Given a Hand to Life J

A long-standing mystery about the ori- gin of life has a new possible solution.

The puzzle is that amino acids, the con- stituents of proteins, occur in two chemi- cally identical forms that have structures mirroring each other like two gloves. Most chemical processes yield left- and right- handed amino acids in equal amounts yet life forms contain left-handed amino acids almost exclusively. New findings show that a mineral common on the ancient Earth might have segregated the mirror- image versions.

Much speculation has focused on ex- traterrestrial influences behind early life. Some scientists suggest that extra left- handed amino acids arrived on mete- orites as life was emerging on Earth (SN: 2/22/97, p. 118). In another theory, Earth formed from dust harboring a primordial excess of left-handed amino acids.

Researchers in Washington, D.C., now report that calcium carbonate, or calcite, can adsorb an excess of left-handed amino acids onto some of its crystal faces and of right-handed amino acids on other faces. Robert M. Hazen and Timo- thy R. Filley of the Carnegie Institution of Washington and Glenn A. Goodfriend of George Washington University report their results in the May 8 PROCEEDINGS OF

“It is very exciting,” says Max Bern- stein of NASA’s Ames Research Center and the SET1 (Search for Extraterrestrial Intelligence) Institute, both in Mountain View, Calif. “Such results provide a plau- sible scenario by which . . . amino acids could be separated from their mirror im- ages, potentially solving a vexing prob- lem of prebiotic chemistry.”

In their analysis, the scientists focused on calcite because it was widely present on the early Earth and is compatible with biological molecules. For instance, it’s the primary ingredient of sea shells.

The researchers placed each of four fist-size calcite crystals in a 50-50 solu- tion of right- and left-handed aspartic acid, an amino acid. Two of the crystals had super-smooth surfaces, and two had microscopic terraces. The scientists found that the terraced crystals ended u p with a 10 percent excess of right- handed amino acids on one type of face and a similar excess of left-handed amino acids on another. The smooth-faced crys- tals tended not to differentiate between the mirror-image forms of aspartic acid.

Hazen speculates that billions of years ago, amino acids might have lined up on crystals’ terraces. They could have then combined into the first all-lefty peptides, or short protein segments.

The calcite results are “of special sig-

THE NATIONAL ACADEMY OF SCIENCES.

Hazen suspects th’at, in fact, that’s A yellowish calcite crystal. what happened. The left-handed amino acids in one place got the edge, he specu- ies bonded into peptides capable of self- lates, because by pure chance, these left- replication. -J. Corrnan

Epileptic seizures may be predictable People with epilepsy typically lead

peaceful lives in the days and hours be- tween their seizures. However, the calm they experience before the mental storms may not be so tranquil after all.

Patterns of mild electrical disturbance in the brains of epilepsy patients seem to foreshadow a seizure hours before its onset, reports a group of neurobiolo- gists and electrical engineers. If the find- ings are confirmed, they may lead to de- vices that would theoretically predict seizures and even halt them before they begin, suggest the researchers in the April NEURON.

Fifty million people around the world- roughly 1 in 100-live with epilepsy. It’s characterized by erratic discharges of electrical activity in the brain. These seizures can set off violent spasms and cause a person to lose consciousness (SN: 6/3/00, p. 384).

“One of the worst aspects of epilepsy is that seizures come without warning,” says Brian Litt of the Hospital of the University of Pennsylvania in Philadelphia, who coau- thored the study with colleagues from the Georgia Institute of Technology and Emory University, both in Atlanta. Although not often directly harmful, a seizure can en- danger a person by unexpectedly occur- ring during an activity, such as driving, that requires control.

Currently, epilepsy patients must take seizure-quelling medications every day. Some complain that these drugs dull the senses and have other side effects.

One potential advantage of prediction is that patients would need medication only in the few hours surrounding an epileptic episode, says Robert Lowen- stein, an epilepsy researcher at Harvard University Medical School in Boston.

Accurate prediction of seizures, he adds, also offers the possibility that an implanted electronic device could stimu- late the brain and defuse seizures before they occur. Lowenstein and others are developing such devices.

Past research focused on detecting a seizure in the few minutes before it oc- curs (SN: 5/23/98, p. 326). Litt decided to take a longer view of the process by us- ing a standard measurement of brain ac- tivity, the electroencephalogram (EEG).

Attracted by the quantitative rigor of industrial engineering, Litt and his col- leagues teamed up with electrical engi- neer George Vachtsevanos and his group, all at Georgia Tech. They usually design failure-detection systems in equipment such as aircraft.

Rosana Esteller of Vachtsevanos’ group had designed a technique for handling large data sets. The researchers exam- ined 3 days’ data from EEG analyses of five epilepsy patients being evaluated for surgery to remove the region of their brain responsible for their seizures.

The researchers found that a series of electrical events anticipated the seizures. Mild energy bursts occurred 7 hours be- fore the seizure, followed 5 hours later by frequent, symptomless seizures too small for the patients to recognize. “It’s like a match that keeps lighting a fuse until fi- nally it catches,” says Litt.

“This is some of the strongest evi- dence to date that [a seizure] can be pre- dicted several hours beforehand,” con- tends Lowenstein.

Litt expects that within only a few years, epilepsy patients will carry brain- implant devices that will both predict and preempt seizures.

-J. Netting

276 SCIENCE NEWS, VOL. 159 MAY 5, 2001