細菌の生産するD-キシロース脱水素酵素の性質

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D-Xylose dehydrogenase (D-xylose : NAD oxidredutase) was demonstrated in the extracts of two strains of D-xylose-dissimilating bacteria, No. 89B and 90A. Strain 89B was thought to belong to the genus Pseudomonas.The enzyme was induced by D-xylose and was highly purified by procedures including chromatographies on DEAE-cellulose, DEAE-Sephadex and Sephadex G-200 and isoelectric focusing on ampholine. The properties of the two enzymes were similar in several respects : optimum pH was 9.0-10.0; optimum temperature for activity was 40-55℃; isoelectric point was 4.79-4.99; molecular weight was 67,000±2,000. Both enzymes exhibited dehydrogenation activity toward D-xylose, L-arabinose, D-glucose and D-galactose with NAD. Activity ratios on these sugars were 100 : 45-81 : 22-47 : 6-3. However, the substrate affinities of the two enzymes differed : K_m values were 2.9,5.9,and 30 mM for D-xylose, L-arabinose and D-xylose, L-arabinose and D-galactose, respectively with strain 89B enzyme, and 0.77 and 100 mM for D-xylose and L-arabinose, respectively with strain 90A enzyme. Both strain 89B and 90A enzymes required NAD and their K_m values were 0.35 and 0.39 mM respectively. The enzymes are thus characterixzed as NAD-dependent D-xylose dehydrogenases relatively broad substrate specificity.
社団法人日本生物工学会の論文