Racemization of Amino Acids in Nature

The amino acids in living organisms are optically active. However, once biologically synthesized amino acids are isolated from the biochemical processes which maintain their optical activity, racemization reactions gradually convert the amino acids into an optically inactive mixture. Racemization proceeds by a very simple reaction, the kinetics and mechanism of which can be easily elucidated. Amino acid racemization on Earth has important applications and implications. The slow racemization of amino acids in fossils and metabolically stable proteins in living mammals can be used to estimate the ages of these materials. Racemization in well-dated fossils can be used to deduce information about the temperature history of the sample. Also, racemization in metabolically stable proteins in living mammals may induce structural changes which in turn affect the functionality of the protein; thus racemization may be part of the ageing process in mammals. Finally, racemization places an important restraint on any proposed mechanisms for the origin of optically active amino acids on Earth since racemization would rapidly convert any optically active amino acids back into an optically inactive or racemic mixture.