Properties of protease in mast cell granules

Abstract

A neutral protease partially purified from rat peritoneal mast cells closely resembled α-chymotrypsin in pH optimum and in susceptibility to several inhibitors including chymostatin, but the two enzymes were quite different in some respects. Mast cell protease was a more basic protein than α-chymotrypsin as indicated by their isoelectric points (9.3 and 8.5, respectively). In contrast to α-chymotrypsin, which consisted of three different subunits, mast cell protease was apparently composed of a single polypeptide chain of molecular weight 27,000 as estimated by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate. Mast cell heparin ionically linked to mast cell protease and suppressed the activity of the enzyme toward N- benzoyl- l-tyrosine ethyl ester and casein by 35 and 75 per cent, respectively, but it did not affect α-chymotrypsin in a medium containing 50 mM CaCl 2. Porcine intestinal mucosa heparin also showed similar inhibitory effects. The inhibitory action of heparin was more evident in low salt medium. Serotonin (0.25 mM), but not histamine, produced an 80 per cent inhibition of mast cell protease (2 μg) activity toward casein in the presence of heparin (2.5 μg). Zn 2+ (0.008–0.2 mM) also suppressed the protease activity by 40–90 per cent in the presence of heparin.