COMMUNICATION /. Biochem. 94, 2071-2074 (1983) Degradation of Neuropeptides by Calcium-Activated Neutral Protease1

The substrate specificity of calcium-activated neutral protease (CANP) from monkey cardiac muscle was examined with various neuropeptides as substrates. The enzyme required mM order calcium ions for activation and had an enkephalinase activity, hydrolyzing Leu-enkephalin at the 'Tyr^Gly and 3Gly-4Phe bonds. Furthermore, it showed the tendency to cleave especially the bonds around the paired basic amino acid residues in a- and /?-neoendorphins and dynorphin(l-13), while it could not hydrolyze substance P. Calcium-activated neutral protease (CANP) is known to exist ubiquitously in various mammalian tissues and appears to be involved in the regulation of various physiological functions through limited proteolysis of biologically important proteins, such as myofibrillar proteins (/, 2), neurofilament pro-teins (3, 4), protein kinases (5, 6), hormone recep-tors (7, 8), etc. It has been reported (9-11) that •CANP tends to hydrolyze only macromolecular proteins and scarcely hydrolyzes smaller peptides and synthetic substrates. In order to understand its physiological function, it seems very important to clarify its substrate specificity. So far, how-ever, not much is known about the substrate specificity of the enzyme. In this study, we ex-amined the substrate specificity of CANP using "various neuropeptides as substrates. CANP was purified from Japanese monkey cardiac muscle as described previously (12). Th