Lysosomal beta-D-mannosidase of rat liver

Mammalian beta-D-mannosidase and beta-mannosidosis

Lysosomal beta-D-mannosidase is the last exoglycosidase involved in the sequential degradation of the N-glycosylproteins glycans. Research on this enzyme was restricted before the discovery of its hereditary deficiency, first in goat (1981) and later in man (1986). We describe the biochemical aspects of these beta-mannosidosis and the properties of the beta-mannosidases of mammalian origin. Our own results concerning human enzyme (from kidney and urine, seminal plasma and blood cells) suggest that, apart from the case of the inherited disease, beta-mannosidase may become a useful tool in other pathologies.

Properties of partially purified goat kidney beta-D-mannosidase

Lysosomal beta-D-mannosidase (EC 3.2.1.25) was purified 6900-fold from normal goat kidney by serial Concanavalin A-Sepharose 4B and Red A dye ligand affinity chromatography, followed by anion exchange and molecular sieve high performance liquid chromatography. The relative molecular mass of the enzyme was estimated by molecular sieving to be 79,000 +/- 3000. The apparent Km for the synthetic substrate, 4-methylumbelliferyl-beta-D-mannopyranoside, was 2.3-2.8 mM and the sharp, unimodal pH optimum was 5.5. Enzyme activity was inhibited by Hg2+, Zn2+, Ag+, Co2+ and the thiol reactive agent N-ethylmaleimide. The mannose derivatives p-nitrophenyl-beta-D- thiomannopyranoside and p-aminophenyl-beta-D-thiomannopyranoside inhibited enzyme activity and may be of use as immobilized ligands in future attempts to purify beta-D-mannosidase by specific affinity chromatography.

Partial purification of goat kidney beta-mannosidase

1. Goat kidney beta-mannosidase was purified 8500-fold to a specific activity of 65,000 nmol/h per mg of protein with a 6% yield by using multiple steps including cation-exchange and anion-exchange fast protein liquid chromatography. This is the first description of a highly purified preparation from goat tissue; however, it was not homogeneous, as judged by silver-stained SDS/polyacrylamide-gel electrophoresis. 2. The enzyme exhibited microheterogeneity when analysed by isoelectric focusing (pI 5.5-6.5). 3. Purified beta-mannosidase hydrolysed the terminal beta-(1----4)-linkage of oligosaccharides that accumulate in beta-mannosidosis.