Characterization of a chymotrypsin-like hydrolytic activity in the opossum kidney cell

To characterize a chymotrypsin-like hydrolytic activity in the cell surface membranes of intact opossum kidney (OK) cells, we partially purified a protease from the membrane fractions of OK cells using Suc-Leu-Leu-Val-Tyr-MCA (Suc, succinyl; MCA, 4-methylcoumaryl-7-amide), a synthetic substrate for chymotrypsin, as the substrate. The semipure enzyme showed seryl chymotrypsin-like characteristics such as preferential hydrolysis of Suc-Leu-Leu-Val-Tyr-MCA and inhibition by phenylmethylsulfonyl fluoride, diisopropylfluorophosphate, and chymostatin. However, it clearly differed from alpha-chymotrypsin in its weak ability to hydrolyze Suc-Ala-Ala-Pro-Phe-MCA and in its high molecular mass (250-300 kDa). The enzyme also had an endopeptidase-like activity in that it cleaved human parathyroid hormone(1-84) at the Leu(37)-Gly(38) and Arg(52)-Lys(53) bonds. These results suggest that a high molecular mass chymotrypsin-like endopeptidase with unique characters is present in the membrane fractions of OK cells.