Abstract
The homochirality of biological amino acids (L-amino acids) or the RNA or DNA backbone ribose (D-sugars) might be established before the origin of life. It has been considered that D-amino acids and L-sugars were eliminated on the primitive earth. Therefore, the presence and function of D-amino acids in living organism have not been studied. However, we have previously shown that Asp-151 and Asp-58 residues invert to the D-beta-isomers at a high degree in alpha A-crystallin from the human eye lens during aging. These modification can cause major changes in structure, since different side chain orientations can induce an abnormal peptide backbone. Similar reactions were also reported in beta-amyloid protein of Alzheimer disease. We suggests that UV irradiation is also closely related to the formation of D-beta-Asp in the protein of lens and skin from elderly person. We propose why racemization/isomerization occurs at specific sites in proteins. [J Radiat Res 44:382 (2003)]
