High selective dehydrogenation of sugar by microbial enzyme

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Substrate specificities of glucose oxidase and galactose oxidase were examined, and their oxidation products were analyzed. It was found that galactose, mannose and xylose were ocidized to the corresponding lactones by glucose oxidase. Maximum yields of lactones were 60% for galactose and 20% for mannose. The C-6 hydroxymethyl group of mathyl D-galactopyranoside was oxidized to corresponding uronic acid via an aldehyde by galactose oxidase. Some oligosaccharides containing galactopyranosyl residues in the molecule were also oxidized by galactose oxidase. Pure and isolated 6'-carboxymelibiose was obtained with a yield of 41% from melibiose and 6"-carboxyraffinose was obtained with a yield of 14% from raffinose. It appears that the C-6 aldehyde of galactopyranosyl group is susceptible to oxidation and is further oxidized to the C-6 carboxyl group in the presence of galactose oxidase. In contrast to the oxidation of galactopyranosyl groups, some sugar alcohols, such as galactitol and xylitol, were oxidized by galactose oxidase to yield L-sugars, such as L-galactose and L-xylose, exclusively. In this case, the L-galactose and L-xylose produced will be stabilized by forming the pyranose ring, and no further oxidation occurs.If carbohydrates are ssimilated aerobically, the total reation can be regarded as the oxidation reaction (multistep dehydrogenation). Stereo, regio or enantiospecific assimilaltion by specific microbes was applied to the high selective separation of carbohydrates which was unable to separate by conventional chemical procedures. D-Allose-assimilating microbes, Rhodotorula rubra KM603, trichosporon cutaneum KM 609 and Acremonium sp. KM 608, obtained by enrichment culture technique from activated sludge, were used to separate the C-2 epimers, , -anomers and DL-mixtures of carbohydrates. Some other specific microbes were evaluated on their selective assimilation.