Transglycosylation reactions of Bacillus stearothermophilus maltogenic amylase with acarbose and various acceptors

It was observed that Bacillus stearothermophilus maltogenic amylase cleaved the first glycosidic bond of acarbose to produce glucose and a pseudotrisaccharide (PTS) that was transferred to C-6 of the glucose to give an α-(1→6) glycosidic linkage and the formation of isoacarbose. The addition of a number of different carbohydrates to the digest gave transfer products in which PTS was primarily attached α-(1→6) to d-glucose, d-mannose, d-galactose, and methyl α-d-glucopyranoside. With d-fructopyranose and d-xylopyranose, PTS was linked α-(1→5) and α-(1→4), respectively. PTS was primarily transferred to C-6 of the nonreducing residue of maltose, cellobiose, lactose, and gentiobiose. Lesser amounts of α-(1→3) and/or α-(1→4) transfer products were also observed for these carbohydrate acceptors. The major transfer product to sucrose gave PTS linked α-(1→4) to the glucose residue. α,α-Trehalose gave two major products with PTS linked α-(1→6) and α-(1→4). Maltitol gave two major products with PTS linked α-(1→6) and α-(1→4) to the glucopyranose residue. Raffinose gave two major products with PTS linked α-(1→6) and α-(1→4) to the d-galactopyranose residue. Maltotriose gave two major products with PTS linked α-(1→6) and α-(1→4) to the nonreducing end glucopyranose residue. Xylitol gave PTS linked α-(1→5) as the major product and d-glucitol gave PTS linked α-(1→6) as the only product. The structures of the transfer products were determined using thin layer-chromatography, high-performance ion chromatography, enzyme hydrolysis, methylation analysis and 13C NMR spectroscopy. The best acceptor was gentiobiose, followed closely by maltose and cellobiose, and the weakest acceptor was d-glucitol.