Introduction to aspartic acid racemization

Before the emergence of life, it is believed that only L-amino acids, and not their specular D-amino acid forms, were chosen for protein formation. Hence, homochirality is essential for life (Motoie et al. 2009). However, in 1936, Kuhn presented kinetic arguments for the inevitable racemization of optically active substances within biological systems and suggested that the accumulation of the wrong stereoisomers could be responsible for the aging process (Helfman et al. 1977). Thus, despite elimination mechanisms and despite the stereospecificity of biosynthetic pathways, some D-amino acids may eventually be incorporated into synthetic enzymes. This would affect the specificity of further synthesis and could culminate in a “quasiautocatalytical collapse” (Kuhn 1958).