Purification and characterization of human metallocarboxypeptidase Z

Carboxypeptidase Z (CPZ) is a recently discovered member of the metallocarboxypeptidase gene family that has an N-terminal domain related to the Wnt/wingless binding domain of frizzled receptors and other proteins. To further characterize the enzymatic properties of CPZ, the enzyme was purified using Arg-and heparin-affinity columns. CPZ has a neutral pH optimum, and is inhibited by chelating agents and several divalent cations (Zn2+, Mn2+, Cd2+, Cu2+, Hg2+). Active site-directed inhibitors of several other metallocarboxypeptidases also inhibit CPZ activity with moderate potency. CPZ cleaves substrates with C-terminal Arg residues, preferring peptides with an Ala in the penultimate position. No activity is detected toward substrates with an Ile-Arg or a Pro-Arg sequence. The Km for dansyl-Phe-Ala-Arg and dansyl-Pro-Ala-Arg are both approximately 2 mM. Taken together, these data suggests a selective role for CPZ in the processing of extracellular peptides or proteins.