D-fructose dehydrogenase of Gluconobacter industrius: purification, characterization, and application to enzymatic microdetermination of D-fructose

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Abstract
D-Fructose dehydrogenase [EC 1.1.99.11] was solubilized and purified from the membrane fraction of glycerol-grown G. industrius IFO 3260 by a procedure involving solubilization of the enzyme with Triton X-100 and subsequent fractionation on diethylaminoethyl-cellulose and hydroxylapatite columns. The purified enzyme was tightly bound to a c-type cytochrome and another peptide existing as a dehydrogenase-cytochrome complex. The purified enzyme was deemed pure by analytical ultracentrifugation and by gel filtration on a Sephadex G-200 column. The MW of the enzyme complex was determined to be about 140,000 and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed the presence of 3 components having MW of 67,000 (dehydrogenase), 50,800 (cytochrome c) and 19,700 (unknown function). Only D-fructose was readily oxidized by the enzyme in the presence of dyes such as ferricyanide, 2,6-dichlorophenolindophenol or phenazine methosulfate. NAD, NADP and O2 did not function as electron acceptors. The optimum pH of D-fructose oxidation was 4.0. The enzyme was stable at pH 4.5-6.0. Stability of the purified enzyme was much enhanced by the presence of detergent in the enzyme solution. Removal of detergent from the enzyme solution facilitated the aggregation of the enzyme and caused its inactivation. An apparent Km for D-fructose was 10-2 M with the purified enzyme. D-Fructose dehydrogenase was a satisfactory reagent for microdetermination of D-fructose.