Non-pancreatic proteases of the chymotrypsin family. II. Two proteases from a mouse mast cell tumor

Abstract

A chymotrypsin-like protease has been prepared from the mouse P815Y mast-cell tumor. It is similar in most respects to the first such enzyme purified from the normal peritoneal mast cells of the rat. It, too, has a molecular weight (estimated by gel filtration) of about 25 000. The apparent molecular weight is lower, unless high salt concentrations are used to overcome affinity of this enzyme for the dextran or polyamide gel columns. The binding of indole, and the binding of potato chymotrypsin inhibitor I, are characteristically strong. Specific alkylations and phosphorylation suggest a serine-histidine active center system. The protein is basic, with strong affinity for the heparin of the mast cell granule. High K + concentrations (>1 M), rather than Na +, are needed to displace fully the enzyme from heparin in solution. A trypsin-like enzyme is also prominent in the mouse (but not the rat) cells. The trypsin-like enzyme has a specificity and active center reactivity characteristic of pancreatic trypsin, and a molecular weight, estimated by gel filtration, of about 35 000.