Enzymic characteristics of the isoenzymes of rat epididymal neutral α-mannosidases and their changes during development in vivo

Three isoenzymic species of neutral alpha-mannosidase (I, II and III) were partially purified from rat epididymis and characterized. Calcium phosphate gel preferentially adsorbed acidic alpha-mannosidase activity, thereby removing the acidic enzyme from the neutral mannosidases. The neutral enzymes, which are of cytosolic origin, require Co2+ for activity, and Mn2+ can substitute partially for Co2+. Mg2+ or Ca2+ had little effect on the activity of the isoenzymes, whereas Zn2+ (100 microM) was a potent inhibitor of the mannosidases. The Km values of mannosidases I, II and III for Co2+ were 10, 10 and 2.7 mM respectively. There was marked alteration of the specific activity of the neutral alpha-mannosidases during epididymal development in vivo. The specific activities of mannosidases I and II were relatively high in the young (24 days) rats, and during the subsequent development the specific activities decreased markedly (approx. 2-3-fold). On the contrary, mannosidase III, which showed relatively low specific activity during 24-45 days of age, increased markedly (approx. 2-fold) as the animals reached adulthood.