Class II α-mannosidase from Aspergillus fischeri: Energetics of catalysis and inhibition

Energetics of the catalysis of Class II α-mannosidase (E.C.3.2.1.24) from Aspergillus fischeri was studied. The enzyme showed Kcat/Km for Man (α1-3) Man, Man (α1-2) Man and Man (α1-6) 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 α1-3, α1-2 and α1-6 linked mannobioses, respectively, reflecting the energy barrier in the hydrolysis of latter two substrates. The enzyme showed Kcat/Km as 3.56 × 105 and 4.61 × 105 M−1 min−1 and Ea as 38.7 and 8.92 kJ/mol, towards pNPαMan and 4-MeUmbαMan, respectively. Binding of Swainsonine to the enzyme is stronger than that of 1-deoxymannojirimycin.