Substrate specificity of bovine liver cytosolic neutral alpha-mannosidase activated by Co2+.
A cytosolic neutral alpha-mannosidase was purified from bovine liver. Its molecular weight was found to be 500,000 on gel filtration. The activity of the enzyme toward Man alpha 1-6-(Man alpha 1-3)Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc-PA was increased 26-fold by preincubation with 1 mM Co2+. Man alpha 1-6(Man alpha 1-3)Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc was hydrolyzed by the enzyme to Man alpha 1-3Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc, which was further hydrolyzed to Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc. The rate of hydrolysis was 15-fold greater than that of Man alpha 1-6(Man alpha 1-3)Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc beta 1-4GlcNAc. This substrate specificity suggested that the enzyme could be involved in the degradation of oligomannose-type sugar chains with one GlcNAc residue released from glycoproteins by endo-beta-N-acetylglucosaminidase, and supported a pathway for glycoprotein catabolism via oligomannosyl glycans with one GlcNAc residue proposed on the basis of an earlier study on a cytosolic neutral alpha-mannosidase from Japanese quail oviduct [Oku, H. and Hase, S. (1991) J. Biochem. 110, 982-989].
Kumano
M
M
Department of Chemistry, Osaka University College of Science.
Omichi
K
K
Hase
S
S
D000117:Acetylglucosamine / Q000737:chemistry; D000818:Animals; D002240:Carbohydrate Sequence; D002417:Cattle; D003035:Cobalt / Q000494:pharmacology*; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation; D006868:Hydrolysis; D008099:Liver / Q000201:enzymology*; D008361:Mannosidases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008362:Mannosides / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity; D043323:alpha-Mannosidase
D008362:Mannosides; D009844:Oligosaccharides; D003035:Cobalt; D008361:Mannosidases; D043323:alpha-Mannosidase; D000117:Acetylglucosamine