Alpha-N-Benzoylarginine-2-naphthylamide hydrolase (cathepsin BI?) from rat skin. III. Substrate specificity, modifier characteristics, and transformation of the enzyme at acidic pH.

Some properties of rat skin benzoylarginine-2-naphthylamide hydrolase types I (preparations I and AI) and II (preparations II and NII) were studied. Both types were activated by dithiothreitol and EDTA, but responded differently to 1 mM KCN, when benzoylarginine-2-naphthylamide (BANA) was used as a substrate: type I was inhibited, while type II was activated. When leucine-2-naphthylamide was used as a substrate, both types were activated by KCN. Thiol proteinase inhibiting substances, like heavy metals, iodoacetic acid, 4-chloromercuribenzoic acid, and tosyllysine chloromethylketone, inhibited the enzymes. Diisopropylfluorophosphate, phenylmethylsulfonyfluoride, 4-aminobenzamidine, and high-molecular-weight trypsin inhibitors were without effect. The substrate specificity of rat skin BANA hydrolase resembled that of an amino acid naphthylamidase, naphthylamides of methionine, lysine, arginine, and alanine being hydrolyzed most rapidly. The rate of hydrolysis of BANA was only 11% of that of methionine naphthylamide. Amino acid esters with a free alpha-amino group were also good substrates. The transformation of type II to type I at acidic pH was studied. During the transformation amino acids or peptides were formed and probably some inhibitor present in type II was destroyed proteolytically.