AM 1, a glycoprotein from the submandibular glands of the mouse, has esterolytic and amidolytic activities

Abstract

The previously isolated female submandibular glycoprotein AM 1 (Nieuw Amerongen, A.V.; Vreugdenhil, A.P. and Roukema, P.A. (1977) Biochim. Biophys. Acta 495, 324–335) has been shown to have hydrolytic activity using N-α- benzoyl- l-arginine ethylester (BAEE) and Chromozym R PK as a substrate. AM 1 can be secreted in vivo by isoproterenol, and to a lesser extent by carbamylcholine and phenylephrine. Based on BAEE as a substrate, AM 1 has an optimum pH of 7.8. In female submandibular glands, about one-third of total esterolytic activity resided in glycoprotein AM 1, but in male submandibular glands, less than 3%. The K m value of glucoprotein AM 1 is 50 μM and its V max is 117 μmol/min per mg glycoprotein AM 1. The enzymatic activity is not inhibited by Ca 2+, Mg 2+ and Na +, slightly by Cu 2+ and strongly by Hg 2+ and phenylmethylsulfonyl fluoride, Glycoprotein AM 1 is capable of hydrolyzing Chromozym R PK with a turnover value 20-fold lower than that for BAEE. With Chromozym R PK as a test substrate, glycoprotein AM 1 was purified by a factor 11. With this substrate, glycoprotein AM 1 has an optimum pH between 6.6 and 7.6 Also with chromozym R PK as a substrate, the submandibular glands of female mouse showed a much higher activity of glycoprotein AM 1 than the submandibular glands of the male mouse. About 75% of all enzymatic activity of female submandibular glands resided in glycoprotein AM 1 and in male submandibular glands 22%. The K m value is 57 μM and its V max 6.7 μmol/min per mg glycoprotein AM 1. From the biochemical characteristics and the localization of glycoprotein AM 1, it has been conclude that glycoprotein AM 1 is not identical to any of the other described murime submandibular esteroproteinases, such as kallikrein, γ-subunit of the nerve growth factor, proteinase A and proteinase F.