Cleavage of CCK 33 by recombinant PC2 in vitro

The specificity and kinetic properties of CCK 33 cleavage by recombinant prohormone convertase 2 (PC2) was investigated using a combination of Sephadex G-50 chromatography, HLPC and RIA methods. It is shown that CCK 33 can be cleaved effectively by PC2 to form CCK 8, the reaction of which has a K(m) of 104.8 microM. No CCK 22 or other products were detected and the reaction is completely inhibited by the PC2 inhibitor, p-CMS (p-chloromercuriphenylsulfonic acid), suggesting that the cleavage is PC2 specific. The time course of this reaction shows an initial lag phase followed by a rapid increase in velocity consistent with a previously reported spontaneous transformation from a 71 kDa relatively inactive form into a more active form of 62 kDa (1). PC2 did not cleave recombinant pro CCK or CCK 1-21. These results demonstrate that PC2, an enzyme usually associated with dibasic cleavages, can cleave easily at single basic residues.