Purification and characterization of a protein containing D-aspartic acid in bovine lens

A protein containing biologically uncommon D-aspartic acid (DAsp) was extracted with 60% EtOH from the water-insoluble fraction of bovine lens. The protein was purified by DEAE-TOYOPEARL chromatography and electrical elution by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) followed by reverse-phase chromatography. The D/L ratio of aspartic acid in the protein isolated was 0.12. The molecular weight of this protein was estimated to be 22,500 by SDS-PAGE. The high content of serine, glycine and glutamic acid was noteworthy. It has been considered that the presence of DAsp in the living body is caused by racemization closely related to aging. The age of bovines used was relatively young (5 years old). If the racemization was caused by aging, the presence of DAsp in the relatively young bovine lens suggested that the aging of the lens protein may start at a relatively young age. The protein containing DAsp may be generally present in lens beyond species such as mouse, bovine and human.