Studies on the Glycosidases in Jack Bean Meal

Abstract α-Mannosidase was purified approximately 500-fold from jack bean meal. This enzyme was able to hydrolyze α-1,6', α-1,2'-, and α-1,3'-linked oligomannosides, but not phenyl-β-d-mannoside and β-1,4'-linked mannobiose. Approximately 5% of the total mannose present in the yeast mannan was set free by α-mannosidase after prolonged incubation. The fact that no sugars other than mannose were detected in the mannan digests indicates that this enzyme is not a polysaccharidase (endoenzyme) in nature. The enzyme hydrolyzes mannobiose, mannotriose, and mannotetraose derived from yeast mannan. The Km values obtained were: p-nitrophenyl-α-d-mannoside, 2.5 x 10-3 m; benzyl-α-d-mannoside, 3.1 x 10-2 m; methyl-α-d-mannoside, 1.2 x 10-1 m. The enzyme was competitively inhibited by mannono-(1 → 4)- and (1 → 5)-lactone. With p-nitrophenyl-α-d-mannoside as substrate, Ki values for (1 → 4)- and (1 → 5)-lactone were 1.0 x 10-2 m and 1.2 x 10-4 m, respectively. α-Mannosidase catalyzes hydrolysis, glycosyl transfer, and synthesis. One of the two disaccharides synthesized from mannose by α-mannosidase was identified as α-1,6'-linked mannobiose.