Subsite affinities of β-glucosidase from Aspergillus sojae on various xylooligosaccharides

Abstract

The subsite affinities of β-glucosidase (EC 3.2.1.21) with high β-xylosidase activity from Aspergillus sojae on various xylooligosaccharides (degree of polymerization: n = 2–6) were investigated by steady-state kinetic analysis. The molecular activity ( k 0) value of the enzyme for xylobiose was not markedly different from those of other substrates ( n = 3–6). The arrangement of the subsite affinities ( A i, i= 1–6) was evaluated; A 1 = 2.93 kcal/mol, A 2 = 3.67 kcal/mol, A 3 = 0.64 kcal/mol, A 4 = 0.12 kcal/mol, A 5 = −0.07 kcal/mol, A 6 = −0.05 kcal/mol, and the intrinsic rate constant ( K int) was 7.6 s −1. The subsite structure was similar to those of β-glucosidase from A. niger and α-glucosidases from A. niger and Mucor javanicus, where the values for A 1 were much larger than those for A 3.