Bioconversion of 1,5-Anhydro-D-fructose to 1,5-Anhydro-D-glucitol and 1,5-Anhydro-D-mannitol Using Saccharomyces cerevisiae

Abstract

1,5-Anhydro-D-fructose (AF) was added to cultures of Saccharomyces cerevisiae and converted to 1,5-anhydro-D-glucitol (AG) and 1,5-anhydro-D-mannitol (AM) by two NADPH-dependent 1,5-anhydro-D-fructose reductase (AFR). The partial amino acid sequence of AFR (AG-forming; AFR-AG) matched with that of D-arabinose dehydrogenase (ArDH). AFR-AG showed reducing activities toward several organic compounds with highest reducing activity toward AF. In addition, it showed oxidizing activity toward several monosaccharides such as D-arabinose and L-xylose. The substrate specificity (reducing activity) and several amino acid sequence motifs of the enzyme resembled those of AFR from mammals. From these enzymatic properties, we concluded that this enzyme should be called AFR rather than ArDH. AFR (AM-forming; AFR-AM) was classified as an oxidoreductase encoded by the ymr315w gene. There was no conserved sequence between AFR-AG and AFR-AM suggesting the existence of two different systems in yeast for converting AF. The AFR-AM (YMR315W-protein) enzyme showed reducing activity only for AF, did not have any oxidizing activity, and has sequence homology only to enzymes of bacterial origin. Finally, we demonstrated an in vitro NADP-NADPH cycling system using the AFR-AG ability to reduce AF and oxidize L-xylose. AG production using low concentration of NADPH increased with the addition of L-xylose.