PMID: 12761304May 23, 2003Paper

Xylose reductase from the Basidiomycete fungus Cryptococcus flavus: purification, steady-state kinetic characterization, and detailed analysis of the substrate binding pocket using structure-activity relationships

Journal of Biochemistry
Peter MayrBernd Nidetzky

Abstract

Xylose reductase has been purified to apparent homogeneity from cell extracts of the fungus Cryptococcus flavus grown on D-xylose as carbon source. The enzyme, the first of its kind from the phylum Basidiomycota, is a functional dimer composed of identical subunits of 35.3 kDa mass and requires NADP(H) for activity. Steady-state kinetic parameters for the reaction, D-xylose + NADPH + H(+)<--> xylitol + NADP(+), have been obtained at pH 7.0 and 25 degrees C. The catalytic efficiency for reduction of D-xylose is 150 times that for oxidation of xylitol. This and the 3-fold tighter binding of NADPH than NADP(+) indicate that the enzyme is primed for unidirectional metabolic function in microbial physiology. Kinetic analysis of enzymic reduction of aldehyde substrates differing in hydrophobic and hydrogen bonding capabilities with binary enzyme-NADPH complex has been used to characterize the substrate-binding pocket of xylose reductase. Total transition state stabilization energy derived from bonding with non-reacting sugar hydroxyls is approximately 15 kJ/mol, with a major contribution of 5-8 kJ/mol made by interactions with the C-2(R) hydroxy group. The aldehyde binding site is approximately 1.2 times more hydrophobic than n-octan...Continue Reading

Citations

Jul 12, 2016·Bioscience, Biotechnology, and Biochemistry·Seiya WatanabeYasuo Watanabe
Jan 13, 2015·Fungal Genetics and Biology : FG & B·Zixuan WangJianping Xu
Nov 6, 2003·Yeast

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