Abstract
SUMMARY: 2-Keto-3-deoxygluconate : NAD 5-oxidoreductase (EC 1.1.1.127) is an enzyme used in pectinolysis by some phytopathogenic bacteria such as Pseudomonas and Erwinia. It converts 2,5-diketo-3-deoxygluconate (DKII) into 2-keto-3-deoxygluconate (KDG) with a concomitant oxidation of NADH. The reaction is reversible in the presence of NAD. The oxidoreductase isolated from Erwinia chrysanthemi was purified 40-fold by protamine treatment, (NH4)2SO4 fractionation, chromatography on DEAE-Sephadex and filtration on Sephadex G-200. The enzyme appeared relatively stable. There was no effect of EDTA or of added ions except Ag+. This ion and the thiol reagent p-chloromercuribenzoate inhibited the enzyme. Other uronic acids, sugars and organic acids tested were neither substrates nor inhibitors of its activity. The optimum pH was 10 for the oxidation of KDG and 7.5 for the reduction of DKII. Both oxidation and reduction reactions showed saturation kinetics with apparent Km values of 7.7 × 10-3 M for KDG and 4 × 10-4 M for NAD (at 37 °C, pH 8.6), and of 3.4 × 10-4 M for DKII and 0.3 × 10-4 M for NADH (at 37 °C and pH 7.0). The enzyme reaction was strongly inhibited by NADH at concentrations higher than 2 × 10-4 M.