Transfer action of alpha-D-xylosidases from Aspergillus flavus MO-5 on p-nitrophenyl-alpha-D-xylopyranoside.

The transfer action of alpha-D-xylosidase I and II from Aspergillus flavus MO-5 on p-nitrophenyl-alpha-D-xylopyranoside (alpha-p-NPX) was investigated, as compared with that of commercial alpha-D-xylosidase (from Bacillus sp.). In reaction mixtures with various concentrations of alpha-p-NPX, both enzymes (I and II) liberated p-nitrophenol and xylose at low concentrations, and showed transfer products in addition to hydrolyzates at high concentrations. IP-1 and IP-3, IIP-1 and IIP-2, and CP-1 and CP-3 were main transfer products by alpha-D-xylosidase I, alpha-D-xylosidase II, and commercial alpha-D-xylosidase, respectively. They were isolated by active charcoal column chromatography and silica gel column chromatography. Their structures were analyzed by enzymatic digestion, methylation analysis, and 13C-NMR analysis. As the results, IP-1, IIP-2, and CP-1 were found to be the same structure, p-nitrophenyl-4-O-(alpha-D-xylopyranosyl)-alpha-D-xylopyranoside. Then, it was proved that the structure of IIP-1 was p-nitrophenyl-3-O-(alpha-D-xylopyranosyl)-alpha-xylopyranoside. On the other hand, IP-3 and CP-3 were found to be the same structure, D-xylopyranosyl-alpha-1,4-D-xylopyranose without a p-nitrophenyl group. We found that alpha-D-xylosidase I showed alpha-1,4 xylosyl transfer action as well as commercial alpha-D-xylosidase, and alpha-D-xylosidase II showed alpha-1,3 xylosyl transfer action in addition to alpha-1,4 xylosyl transfer action on alpha-p-NPX.