Enzymatic synthesis of β-xylanase substrates: transglycosylation reactions of the β-xylosidase from Aspergillus sp

A β- d-xylosidase with molecular mass of 250±5 kDa consisting of two identical subunits was purified to homogeneity from a cultural filtrate of Aspergillus sp. The enzyme manifested high transglycosylation activity in transxylosylation with p-nitrophenyl β- d-xylopyranoside (PNP-X) as substrate, resulting in regio- and stereoselective synthesis of p-nitrophenyl (PNP) β-(1→4)- d-xylooligosaccharides with dp 2–7. All transfer products were isolated from the reaction mixtures by HPLC and their structures established by electrospray mass spectrometry and 1H and 13C NMR spectroscopy. The glycosides synthesised, β-Xyl-1→(4-β-Xyl-1→) n 4-β-Xyl-OC 6H 4NO 2- p ( n=1–5), were tested as chromogenic substrates for family 10 β-xylanase from Aspergillus orizae (XynA) and family 11 β-xylanase I from Trichoderma reesei (XynT) by reversed-phase HPLC and UV-spectroscopy techniques. The action pattern of XynA against the foregoing PNP β-(1→4)- d-xylooligosaccharides differed from that of XynT in that the latter released PNP mainly from short PNP xylosides (dp 2–3) while the former liberated PNP from the entire set of substrates synthesised. Graphic