Structural and functional properties of aldose xylose reductase from the D-xylose-metabolizing yeast Candida tenuis

The primary structure of the aldose xylose reductase from Candida tenuis (C tAR) is shown to be 39% identical to that of human aldose reductase (hAR). The catalytic tetrad of hAR is completely conserved in CtAR (Tyr51, Lys80, Asp46, His113). The amino acid residues involved in binding of NADPH by hAR (D.K. Wilson, et al., Science 257 (1992) 81-54) are 64% identical in CtAR. Like hAR the yeast enzyme is specific for transferring the 4-pro-R hydroge n of the coenzyme. These properties suggest that CtAR is a member of the al do/keto reductase superfamily. Unlike hAR the enzyme from C. tenuis has a d ual coenzyme specificity and shows similar specificity constants for NADPH and NADH. It binds NADP(+) approximately 250 times less lightly than hAR. T ypical turnover numbers for aldehyde reduction by CtAR (15-20 s(-1)) are up to 100-fold higher than corresponding values for hAR, probably reflecting an overall faster dissociation of NAD(P)(+) in the reaction catalyzed by th e yeast enzyme. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.