A CLUE to the mystery of how nature selected left-handed amino acids rather right-handed ones may lie in the way the substances behave as they dissolve in water.
Amino acids can appear in left-handed (L) and right-handed (D) mirror-image forms. When made from scratch in the lab the two versions are equally likely to appear, but in nature, L amino acids dominate.
Donna Blackmond at Imperial College London and colleagues dissolved a mixture of solid L and D versions of the amino acid serine in water. They found that a small difference in the initial proportion of one version gets amplified in the resulting solution. So a 100:1 mixture of L- and D-serine produces a solution made up almost entirely of L-serine, but so does a 100:99 mixture (Nature, vol 441, p 621).
"It doesn't matter what proportions of solid amino acids you throw in, you always get exactly the same proportions in solution," says Blackmond, whose team has found a similar effect with other amino acids. She says she is surprised that no one noticed the effect before.
This effect could have amplified a slight excess of L-amino acids in nature. Why there was a slight excess to start with is another question.
