Separation, characterization, and specificity of alpha-mannosidases from Vigna umbellata

Information about the specificity of glycosidase enzymes is important since it affects their use for characterization and synthesis of oligosaccharides. Two alpha-mannosidases (EC 3.2.1.24), I and II, were isolated from rice beans (Vigna umbellata). The native molecular weight of both isozymes was estimated to be 329,000, but pIs of form I were 5.03-5.34 and pIs of form II were 5.46-6.20. The two isozymes were characterized in terms of optimal pH and temperature, effects of metal ions, inhibition by swainsonine and 1-deoxymannojirimycin, and kinetic parameters for p-nitrophenyl-alpha-D-mannopyranoside and Man alpha (1-2)Man. Both enzymes were more specific towards Man alpha (1-2)Man in both hydrolysis and synthesis, but their hydrolytic specificities towards Man alpha (1-3)[Man alpha (1-6)]Man were different.