The substrate specificity of bovine and feline lysosomal alpha-D-mannosidases in relation to alpha-mannosidosis.
Lysosomal alpha-mannosidases were partially purified from bovine and feline liver and employed to digest a large number of oligosaccharides with structures corresponding to the oligomannosyl parts of complex, hybrid, and high-mannose glycans. The incubation products were identified by high pressure liquid chromatography with reference compounds of defined structure and by acetolysis. For all classes of substrates, the lysosomal alpha-mannosidases displayed a high degree of in vitro specificity with regard to the hydrolysis of mannose residues. Thus, in each case, 1 or at most 2 residues were always preferentially cleaved so that the degradative process proceeded down a well defined pathway. A comparison of the relative efficiency with which lysosomal alpha-mannosidases catalyzed the hydrolysis of particular oligosaccharides and of the structures of the resulting intermediates with those of the compounds accumulated in alpha-mannosidosis allows conclusions to be drawn regarding the nature of the enzymatic defect. In bovine alpha-mannosidosis, the oligosaccharides are those expected for a partial deficiency of normal lysosomal alpha-mannosidase, so that they correspond to intermediates in the normal catabolic pathway. In feline alpha-mannosidosis, in which the alpha-mannosidase deficiency is more severe than in cattle, the accumulated oligosaccharides primarily represent intact oligomannosyl moieties of N-linked glycans rather than the products of residual alpha-mannosidase activity.
DeGasperi
R
R
Carbohydrate Unit, Lovett Laboratories, Harvard Medical School, Charlestown, Massachusetts.
al Daher
S
S
Daniel
P F
PF
Winchester
B G
BG
Jeanloz
R W
RW
Warren
C D
CD
D000818:Animals; D002240:Carbohydrate Sequence; D002415:Cats; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D008099:Liver / Q000201:enzymology; D008247:Lysosomes / Q000201:enzymology*; D008358:Mannose / Q000378:metabolism; D008361:Mannosidases / Q000378:metabolism*; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000378:metabolism; D011134:Polysaccharides / Q000378:metabolism; D013379:Substrate Specificity; D043323:alpha-Mannosidase; D008363:alpha-Mannosidosis / Q000201:enzymology*
D009844:Oligosaccharides; D011134:Polysaccharides; D008361:Mannosidases; D043323:alpha-Mannosidase; D008358:Mannose