Transxylosylation of β-Xylosidase from Aspergillus awamori K4

Abstract

β-Xylosidase from Aspergillus awamori K4 was purified. The optimum pH and temperature were around pH 4 and 70°C, and the molecular weight was estimated to be 117, 000 on SDS-PAGE analysis. The enzyme has broad acceptor specificity in transxylosylation. Especially, its acceptor accessibility for sorbitol and mannitol of sugar alcohols were higher than that for monosaccharides. Trehalose was a much more effective acceptor than maltose and lactose of other disaccharides. In the reaction with 13-14% xylooligosaccharides (consisting of 3.4% xylose, 67.9% xylobiose, and 28.7% xylotriose) and 9-13% acceptors (sorbitol, mannitol, and trehalose), the amount of transfer products for each acceptor was 7-11%, in 24 h. On ¹H- and ¹³C-NMR analysis, main transfer products with sorbitol and mannitol were 6-O-β-xylosyl sorbitol (77.3%) and 1(6)-O-β-xylosyl mannitol (73.7%), respectively. Two products with trehalose were 6(6')-O-β-xylosyl trehalose (52.1%) and 6, 6'-O-β-di-xylosyl trehalose (47.9%).