Class II alpha-mannosidase from Aspergillus fischeri: energetics of catalysis and inhibition.

Energetics of the catalysis of Class II alpha-mannosidase (E.C.3.2.1.24) from Aspergillus fischeri was studied. The enzyme showed Kcat/Km for Man (alpha1-3) Man, Man (alpha1-2) Man and Man (alpha1-6) Man as 7488, 5376 and 3690 M(-1) min(-1), respectively. The activation energy, Ea was 15.14, 47.43 and 71.21 kJ/mol for alpha1-3, alpha1-2 and alpha1-6 linked mannobioses, respectively, reflecting the energy barrier in the hydrolysis of latter two substrates. The enzyme showed Kcat/Km as 3.56x10(5) and 4.61x10(5) M(-1) min(-1) and Ea as 38.7 and 8.92 kJ/mol, towards pNPalphaMan and 4-MeUmbalphaMan, respectively. Binding of Swainsonine to the enzyme is stronger than that of 1-deoxymannojirimycin.