Studies on esteroproteases in the mouse submaxillary gland

Purification and properties of the isozymes

Abstract

Recently we have reported that these was a marked strain difference in arginine-specific esteroprotease isozymes found in the submaxillary gland of inbred mice. The present study was designed to clarify the properties of the esteroprotease isozymes in the submaxillary gland of mice.
Three esteroproteases (isozymes III, N and IX) and two esteroproteases (isozymes VI and VIII) were purified from the two strains, BALB/cA and DBA/2N male mice, respectively, by gel filtration and column isoelectric focusing. Each of the purified isozymes appeared as a single protein band with polyacrylamide gel electrophoresis.
The isoelectric points of the five isozymes were 5.6, 5.9, 7.6, 8.8 and 9.8 in isozymes III, IV, VI, VIII and IX, respectively. The five isozymes had a common molecular weight of about 28, 000 and the activities to hydrolyze α-N-benzoyl-L-arginine ethyl ester were not reduced by treating them for 1 hour at 40°C.
Although a marked difference was found in substrate specificity when tested with various synthetic substrates, amino acid compositions of the enzymes closely resembled each other among the five isozymes.