Mammalian glycosidases. 2. Properties of α-mannosidase and β-galactosidase from rat epididymis

Abstract

P-Nitrophenyl [alpha]-mannoside and phenyl-[alpha]-mannoside were substrates for [alpha]-mannosidase and o-nitrophenyl-[beta]-galactoside and phenyl-[beta]-galactoside were substrates for [beta]-galactosidase. The pH optimum of [alpha]-mannosidase in various buffers and for both substrates with 5.0. The pH optimum of [beta]-galactosidase in acetic acid NaOH buffer with the nitrophenyl substrate was 2.9; in citric acid NaOH phosphate-citrate buffers with the nitrophenyl substrate, and in acetic acid NaOH buffer with the phenyl substrate, 2 optima were obtained, at pH 2.9 and 3.5. Mean Km values obtained were: p-nitrophenyl-[alpha]-mannoside 13 m[image], phenyl-[alpha]-mannoside 57 m[image], o-nitrophenyl-[beta]-galactoside 0.38 m[image] and phenyl-B[beta]-galactoside 1.6 m[image]. When kept at 37[degree] for 1 hr., a-mannosidase was stable over the pH range 5.0-6.5 and [beta]-galactosidase over the pH range 3.0-7.0. Heating at 70[degree] for 5 min. destroyed [beta]-galactosidase activity, and similar treatment at 75[degree] destroyed a-mannosidase activity. a-Mannosidase was stable at 55-60[degree] for 5 minutes. Mean K, values for mannono-1->4-lactone, a specific competitive inhibitor of a -mannosidase, were 11 m[image] with p-nitrophenyl-a-mannoside as substrate and 19 m[image] with phenyl-[alpha]-mannoside as substrate. Mean K, values for galactono-1-4-lactone, a competitive inhibitor of B-galactosidase, were 0.51 m[image] with o-nitrophenyl-[beta]-galactoside as substrate and 0.21 m[image] with phenyl-[beta]-galactoside as substrate. Both enzymes are strongly inhibited by Ag+ and Hg++ in low concentrations; Cu++ are powerful inhibitors of [alpha]-mannosidase activity and moderate inhibitors of [beta]-galactosidase activity.