The Modes of Action of Two Endo-1, 4-β-_D-Xylanases from Aspergillus sojae on Various Xylooligosaccharides

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The modes of action of two endo-1, 4-β-_D-xylanases(X-I and X-II-B)from Aspergillus sojae were investigated using xylooligosaccharides and their corresponding alditols. Due to the dependence of the molecular activity(k_0)on the degree of polymerization of substrates, it was suggested that each xylanase had five subsites. With regard to the bond-cleavage frequencies of various xylooligosaccharide-alditols, the catalytic site of each xylanase was located between the third and fourth subsites, counting from the terminal site, which was attached to the non-reducing end of the substrates. The intrinsic rate constants(k_<int>)for the hydrolysis of glycosidic linkages of X-I and X-II-B were calculated to be 56 and 43_S^<-1> respectively. Evaluation of subsite affinities of each xylanase:the total subsite affinity of (A_3+A_4), adjacent to the catalytic site of X-I, had a positive value(0.10 kcal/mol), whereas that of X-II-B had a negative value(-0.39 kcal/mol). The other subsite affinities of X-I exhibited higher values than that of X-II-B, except for the subsite affinity of A_1.
社団法人日本生物工学会の論文
1998-03-25