1. 1.|Cathepsin B2 was purified 3900-fold over homogenate with respect to the hydrolysis of N-benzoyl-l-arginine amide (Bz-Arg-NH2). Cathepsin B2 was shown to be a relatively nonspecific carboxypeptidase by virtue of its hydrolysis of N-blocked dipeptides. Only N-blocked dipeptides that contained proline, sarcosine, β-alanine, or d-amino acids were not hydrolyzed, which indicates a specificity for α-l-amino acids. The optimum hydrolysis of Bz-Arg-HN2 and N-blocked dipeptides by cathepsin B2 occurred at pH 5.5-5.6, with Km values in the range of 10-15 mM. Dipeptides were not hydrolyzed by cathepsin B2, but some tripeptides were hydrolyzed. A tetrapeptide (Leu-Trp-Met-Arg), a hexapeptide (Leu-Trp-Met-Arg-Phe-Ala), and glucagon were hydrolyzed by cathepsin B2 with the release of amino acids from the carboxyl terminus. Insulin A chain, insulin B chain, and bradykinin were ot hydrolyzed by cathepsin B2, perhaps owing to the presence of cysteic acid or proline residues near the carboxyl terminus. No endopeptidase activity of cathepsin B2 was found. Cathepsin B2 was activated by sulfhydryl compounds and inhibited by p-hydroxymercuribenzoate.
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