Non-enzymatic, post-translational, amino acid modifications in ageing. A brief review.

Accumulated evidence implicates two non-enzymatic, post-translational, amino acid modifications -- deamidation of asparagine and glutamine, and racemization of aspartic acid -- as potentially important reactions in cellular and organismal ageing. Rates of deamidation can be genetically regulated over a range of at least six days to ten years, and this release of ammonia from amides causes molecular conformational changes, loss of activity, and age-related alterations in a number of proteins in vivo. Racemized aspartic acid amasses with age, especially in croslinked and partly degraded proteins of the normal ageing human lens and yellow cataracts. In both cases, modification of amino acids could account for the accumulation of altered proteins observed with ageing in the cells of certain organisms.