Acidic isozyme of a chymotrypsin-like esteroprotease from mouse submandibular gland

An acidic isozyme of a chymotrypsin-like esteroprotease from the mouse submandibular gland was purified and its properties were compared with those of the basic isozymes purified previously (Takuma, T., et al. (1983) Biochim. Biophys. Acta 755, 70-75), bovine pancreatic alpha-chymotrypsin, and other chymotrypsin-like enzymes of mice. The isoelectric point of the purified enzyme was pH 4.7, and the molecular weight was estimated to be 25,000 by gel filtration on Sephadex G-100. The enzyme hydrolyzed benzoyl-L-tyrosine ethyl ester (Bz-Tyr-OEt) 7 times more slowly than basic isozymes did, but hydrolyzed casein as slowly as the basic isozymes did. The acidic isozyme was 40 times more sensitive to chymostatin than basic isozymes were, but 10 times less sensitive than alpha-chymotrypsin was. Moreover, acidic and basic isozymes were immunologically distinct. Chymotrypsin-like esteroproteases in the submandibular gland were antigenically unique among chymotrypsin-like enzymes in various tissues of mice.