Epidermal proteinases in the European eel.

A fluorescent-sensitive assay demonstrated the exhaustive detection of proteinase activities in the dorsal skin of the European eel. Two distinct skin extracts were prepared from skin mucus and epidermal cell layers with no mutual contamination, so that the latter extract contained significant susceptibility of all tested substrates. Optimum hydrolysis pH's for susceptible substrates were found in acidic and neutral ranges, and optimum hydrolysis temperatures for the same substrates fell mainly in the 40 degrees-50 degrees C range. In addition, diverse inhibitory influences on these hydrolyses were prompted by several proteinase inhibitors and metal chlorides, and some other reagents specifically affected the individual hydrolysis; among them, the inhibitions of all activities by p-tosyl-L-phenylalanyl-chloromethylketone CdCl2, CuCl2, HgCl2, and ZnCl2 were remarkable. Antipain, iodoacetamide, and CoCl2 induced a severe inhibition of all except three activities, whereas N-ethylmaleimide markedly inhibited only these three activities. These findings suggest that epidermal cell layers of the European eel retain a party of proteolytic enzymes, and this party is judged from their exhibiting specificities to be composed of four distinct proteinases, presumably cathepsins L and B, a serine proteinase, and an aminopeptidase.