SPECIFIC RACEMIZATION AND ISOMERIZATION OF THE ASPARTYL RESIDUE OF ALPHA-A-CRYSTALLIN DUE TO UV-B IRRADIATION

We have reported that the aspartyl(Asp)-151 residue in alpha A-crystal lin in human eye lens was inverted to the D-isomer and isomerized to b eta-Asp residue with age. We report here that ultraviolet (UV)-B irrad iation induces the racemization and isomerization of the Asp-151 resid ue of alpha A-crystallin from lenses of 6-week-old rats to form D-isom er and beta-Asp residue. Simultaneous racemization and isomerization o f the specific Asp residue indicate that the reaction proceeds via for mation of a succinimide intermediate. This modification was not observ ed in UV-A irradiated and normal lenses. UV-B irradiation induced the racemization of only the Asp-151 residue and did not affect the other Asp residues in alpha A-crystallin. On the other hand, the high molecu lar weight fraction of the lens protein increased upon UVB irradiation . Modification of the Asp residue would affect the three-dimensional p acking array of the lens protein. (C) 1997 Academic Press Limited.