AM1, a glycoprotein from the submandibular glands of the mouse, has esterolytic and amidolytic activities

The previously isolated female submandibular glycoprotein AM1 ( 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-alpha-benzoyl-L-arginine ethylester (BAEE) and ChromozymR PK as a substrate. AM1 can be secreted in vivo by isoproterenol, and to a lesser extent by carbamylcholine and phenylephrine. Based on BAEE as a substrate, AM1 has an optimum pH of 7.8. In female submandibular glands, about one-third of total esterolytic activity resided in glycoprotein AM1, but in male submandibular glands, less than 3%. The Km value of glycoprotein AM1 is 50 microM and its Vmax is 117 mumol/min per mg glycoprotein AM1. The enzymatic activity is not inhibited by Ca2+, Mg2+ and Na+, slightly by Cu2+ and strongly by Hg2+ and phenylmethylsulfonyl fluoride. Glycoprotein AM1 is capable of hydrolyzing ChromozymR PK with a turnover value 20-fold lower than that for BAEE. With ChromozymR PK as a test substrate, glycoprotein AM1 was purified by a factor of 11. With this substrate, glycoprotein AM1 has an optimum pH between 6.6 and 7.6. Also with chromozymR PK as a substrate, the submandibular glands of female mouse showed a much higher activity of glycoprotein AM1 than the submandibular glands of the male mouse. About 75% of all enzymatic activity of female submandibular glands resided in glycoprotein AM1 and in male submandibular glands 22%. The Km value is 57 microM and its Vmax 6.7 mumol/min per mg glycoprotein AM1. From the biochemical characteristics and the localization of glycoprotein AM1, it has been concluded that glycoprotein AM1 is not identical to any of the other described murine submandibular esteroproteinases , such as kallikrein, gamma-subunit of the nerve growth factor, proteinase A and proteinase F.