Substrate specificity of the bovine and feline neutral alpha-mannosidases.
Neutral alpha-mannosidases were prepared from bovine and cat liver. The activities were distinguished from lysosomal and Golgi alpha-mannosidases by their neutral pH optima, relatively low Km for their synthetic substrate p-nitrophenyl alpha-D-mannoside, inhibition by Zn2+ and absence of inhibition by Co2+, EDTA, low concentrations of swainsonine, or deoxymannojirimycin. The cytosolic alpha-mannosidases were not retained by concanavalin A-Sepharose. They were able to degrade efficiently a variety of oligosaccharides with structures corresponding to certain high-mannose glycans or the oligomannosyl parts of hybrid and complex glycans. However, unlike lysosomal alpha-mannosidases from the same species these enzymes were not able to degrade Man9GlcNAc2 efficiently, and the bovine neutral alpha-mannosidase was not able to degrade a hexasaccharide with a structure analogous to Man5GlcNAc2-PP-dolichol. Sharp differences were noted for the bovine and cat enzymes with regard to the specificity of degradation. The bovine neutral alpha-mannosidase degraded the substrates by defined pathways, but the cat neutral alpha-mannosidase often produced complex mixtures of products, especially from the larger oligosaccharides. Therefore the bovine enzyme resembled the rat and human cytosolic alpha-mannosidases, but the cat enzyme did not. The bovine and cat neutral alpha-mannosidases, unlike the corresponding lysosomal activities, did not show specificity for the hydrolysis of the (1----3)- and (1----6)-linked mannose residues in the N-linked glycan pentasaccharide core.
De Gasperi
R
R
Lovett Laboratories, Department of Biological Chemistry, Harvard Medical School, Charlestown, MA.
al Daher
S
S
Winchester
B G
BG
Warren
C D
CD
D000818:Animals; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002415:Cats; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008361:Mannosidases / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000302:isolation & purification / Q000378:metabolism*; D013045:Species Specificity; D013379:Substrate Specificity; D043323:alpha-Mannosidase
D009844:Oligosaccharides; D008361:Mannosidases; D043323:alpha-Mannosidase