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

Abstract

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.

Kex2 protease converts the endoplasmic reticulum α1,2-mannosidase of Candida albicans into a soluble cytosolic form

“…In lower eukaryotes, cytosolic α -mannosidase activity has not been reported; however, in mammals these enzymes have been studied extensively ( Dutta & Majumder, 1984 ; Tulsiani & Touster, 1987 ; Haeuw et al , 1991 ; De Gasperi et al , 1992 ). These neutral cytosolic α -mannosidases participate in the hydrolysis of free N -oligosaccharides, which are generated by the ERAD of misfolded N -glycoproteins and by cleavage of dolichol-linked oligosaccharides ( Spiro, 2004 ; Suzuki et al , 2006 ).…”

“…These neutral cytosolic α -mannosidases participate in the hydrolysis of free N -oligosaccharides, which are generated by the ERAD of misfolded N -glycoproteins and by cleavage of dolichol-linked oligosaccharides ( Spiro, 2004 ; Suzuki et al , 2006 ). This activity is not sensitive to 1-deoxymannojirimycin (1-DMJ), but is inhibited by swainsonine ( Tulsiani & Touster, 1987 ; Haeuw et al , 1991 ) and activated by Co 2+ ( Dutta & Majumder, 1984 ; Haeuw et al , 1991 ; De Gasperi et al , 1992 ; Weng & Spiro, 1996 ). Two cytosolic α -mannosidases have been described in rat liver.…”

Inhibitory effect of zinc on stimulated erythropoietin synthesis in HepG2 cells

“…Moreover, other examples even reveal that Co2+ and Zn2+ can have opposite effects on proteins. These are enzymes such as the z-mannosidase from rat epididymis (Dutta & Majumder, 1984), the alkaline phosphatase from bovine polymorphonuclear neutrophils (Yasuura et al, 1985) or the hepatic UDP-glucuronosyltransferase (Aitio et al, 1980), whose activities could be stimulated by Co2+, but were inhibited by Zn2+. Therefore it is possible not only that does zinc have no stimulating effect on EPO synthesis, but also that it may inhibit the stimulation of EPO synthesis by other metal ions or hypoxia.…”