Abstract
Dor L-amino acids, regardless of their state (peptide-bound or free, in the solid state or in aqueous solution), tend to racemize. In a living cell this racemization is usually compensated by specific degradation and replacement of the unwanted polypeptides that contain the wrong enantiomers. But a few long-lived proteins that are synthesized at or near birth are never replaced. Well investigated is the racemization of L-aspartic acid at a rate of 0.1 to 1.14 per cent per year in proteins from lenses and dentine. Increased racemization of eye lens proteins has been related to a form of human eye disease known as brunescent cataracts. Also quite well investigated is the racemization of amino acids in fossil proteins. The time and temperature dependence of racemizations has found various applications in the determination of the ages of long-lived individuals and in the investigation of the ages and the tempe<ature history of younger fossils. For prebiotic peptide synthesis no practicable mechanism that leads to the exclusion of the unwanted optical antipodes has as yet been found. Peptides (in particular dipeptides) in aqueous solution generally racemize about as fast as free amino acids. In thermal polymerization of amino acids racemization often proceeds faster than polymerization. Some new data on the racemization of amino acids during thermal peptide synthesis will be presented.
Published Version
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