An electrophoretic investigation of the cytosolic di- and tripeptidases of fish: molecular weights, substrate specificities, and tissue and phylogenetic distributions.

The cytosolic di- and tripeptidases of fish were studied in an electrophoretic phylogenetic survey that included elasmobranchs, a holostean, and teleosts. Antisera against four of the peptidases from tuna were raised in rabbits and used to establish homologies between the peptidases of tuna and other fish and between piscine PEP A, B, and S and corresponding enzymes of the higher vertebrates. Substrate specificities, tissue distributions, and electrophoretic mobilities were conserved during the evolution of the fish. The nomenclature for mammalian peptidases was extended to the piscine enzymes, but with reservations in the case of PEP C and E. Using this nomenclature, the six major, genetically independent peptidases are PEP A, B, C, D, E, and S. Within the fish substrate specificity was a reliable indicator of identity. The peptidases of vertebrates thus consist of a widely distributed group of enzymes with constant characteristics. Much of the confusion in the field is probably due to variable and poorly defined species-specific enzymes.