Amino acid lends a heavy hand.

Billions of years ago, a simple amino acid may have triggered all other amino acids to adopt a left-handed configuration, determining the chemical fate of these biological building blocks and influencing the emergence of life on Earth.

Amino acids, the basic units of proteins, come in either right- or left-handed configurations--mirror images of each other. However, the amino acids in living organisms are all lefties. To find out why, R. Graham Cooks and his colleagues at Purdue University in West Lafayette, Ind., analyzed all 20 natural amino acids and found that only serine forms highly chemically stable clusters.

"Even more dramatic, the amino acids in each cluster were either all in the right or left form," says Cooks. In contrast, clusters of other amino acids, were less stable and contained a mixture of both left and right configurations, Cooks and his colleagues report in the Aug. 4 Angewandte Chemie International Edition.

When the researchers mixed clusters of eight left-handed serines with other amino acids, the clusters bound only to other left-handed amino acids. Similarly, right-handed serine clusters bound only to right-handed amino acids. When the researchers exposed serine clusters to simple sugars, just the opposite occurred. Left-handed serine bound only to right-handed sugars and vice versa.

Serine dusters' high stability and selectivity have convinced the researchers that left-handed serine must have forced its chemical siblings to follow its lead. What caused serine's left form to become dominant in the first place remains an open question. Some scientists say that ancient minerals may have favored one form over the other (SN: 5/5/01, p. 276). Others point to the effects of radiation hitting primordial Earth. Or, says Cooks, it could have happened by chance.--A.G.