Enzymatic redox isomerization of 1,6-disaccharides by pyranose oxidase and NADH-dependent aldose reductase

Pyranose 2-oxidase, a homotetrameric FAD-flavoprotein from the basidiomycete Trametes multicolor, catalyzes regioselectively the oxidation of the 1 --> 6 disaccharides allolactose [beta -D-Gal p-(1 --> 6)-D-Glc], gentiobiose [beta -D-Glc p-(1 --> 6)-D-Glc], melibiose [alpha -D-Gal p-(1 --> 6)-D-Glc], and isomaltose [alpha -D-Glc p-(1 --> 6)-D-Glc] at position C-2 of their reducing moiety, The resulting glycosyl D-arabino-hexos-2-uloses can be reduced specifically at C-l by NAD(P)H-dependent aldose reductase from the yeast Candida tenuis. By this novel, two-step redox isomerization process the four disaccharide substrates could be converted to the corresponding keto-disaccharides allolactulose [beta -D-Gal p-(1 --> 6)-D-Fru], gentiobiulose [beta -D-Glc p-(1 --> 6)-D-Fru], melibiulose [alpha -D-Gal p-(1 --> 6)-D-Fru], and isomaltulose (palatinose, [alpha -D-Glc p-(1 --> 6)-D-Fru]) in high yields. These products could find application in food technology as alternative sweeteners. (C) 2001 Elsevier Science B.V. All rights reserved.