Soluble exopeptidases of bovine and human lens: characterization by electrophoresis

Soluble exopeptidases present in bovine and human lenses were identified and characterized using starch gel electrophoresis separation followed by activity staining with an L-aminoacid oxidase/peroxidase system or a naphthylamine fluorescence system. Sixteen peptide and twelve naphthylamide substrates were used. The profile of substrate specificities for each electrophoretically separated exopeptidase was determined. Characterization also included the effects on activity of pH, EDTA, puromycin, and divalent cations. In addition, molecular weight determinations by gel filtration were made. Six bovine lens peptidases were identified including leucine aminopeptidase and dipeptidylpeptidase III and six human lens peptidase including dipeptidylpeptidase III. Strong homology in terms of substrate specificity and molecular weight was seen between bovine leucine aminopeptidase and one of the human peptidases previously designated peptidase "S". The findings indicate the diversity of exopeptidase available for polypeptide degradation in lens.