Properties of the NAD(P)H-dependent xylose reductase from the xylose-fermenting yeast Pichia stipitis

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Abstract
Xylose reductase from the xylose-fermenting yeast Pichia stipitis was purified to electrophoretic and spectral homogeneity via ion-exchanges, affinity and high-performance gel chromatography. The enzyme was active with various aldose substrates, such as DL-glyceraldehyde, L-arabinose, D-xylose, D-ribose, D-galactose and D-glucose. Hence the xylose reductase of Pichia stipitis is an aldose reductase. Unlike all aldose reductases characterized so far, the enzyme from this yeast was active with both NADPH and NADH as coenzyme. The activity with NADH was .apprx. 70% of that with NADPH for the various aldose substrates. NADP was a potent inhibitor of both the NADPH- and NADH-linked xylose reduction, whereas NAD showed strong inhibition only with the NADH-linked reaction. These results are discussed in the context of the possible use of Pichia stipitis and similar yeasts for the anaerobic conversion of xylose into ethanol.