Characterization of two esteroproteases from the male mouse submandibular gland

Three major esteroproteases, proteases A and D and P-esterase, obtained from the glands were studied kinetically and chemically; two (proteases A and D) were identified. Protease A is composed of a single subunit, molecular weight (27,600) similar to the native molecule (27,000); protease D consists of three subunits, approximate molecular weights of 9200, 7600 and 4600. P-esterase contains two subunits, approximate molecular weights of 7100 and 14,000. Protease A exhibits a strong kinin-releasing activity; the other two enzymes have low activity. Protease D binds to low molecular weight-epidermal growth factor, forming a complex which has an electrophoretic mobility similar to that of high molecular weight-epidermal growth factors. When beta-nerve growth factor was incubated with protease A, the amino-terminal amino acid, serine, was lost from the growth factor and a new amino-terminal amino acid, methionine, appeared. These data indicate that proteases D and A are the same proteins as epidermal growth factor-binding protein and beta-nerve growth factor endopeptidase, respectively. From a comparison of the peptide maps of trypsin-digests of the enzymes, the proteases A and D were inferred to have a similar primary structure.