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Metabolic Consequences of a Block in the Synthesis of 5-Keto-D-Fructose in a Mutant of Gluconobacter cerinus

^a Department of Biochemistry, Albert Einstein College of Medicine, Yeshiva University, New York, New York 10461

ABSTRACT

A mutant of Gluconobacter cerinus var. ammoniacus, IFO 3267, has been isolated which is deficient with respect to fructose 5-dehydrogenase, the enzyme catalyzing the oxidation of D-fructose to 5-keto-D-fructose (5 KF). Growth of this mutant on fructose as the sole carbon source was impaired unless the culture medium was supplemented with 5 KF. Significant randomization of the 1 and 6 positions of fructose has been reported previously for the wild-type organism during growth on this ketohexose. The pattern of ³H incorporation into the C5 position of ribonucleic acid-ribose when the mutant was grown on [1-³H]fructose and [6-³H]fructose in the presence of 5 KF indicated that such randomization did not occur in this variant. The randomization observed in the wild type is, therefore, a consequence of the partial oxidation of fructose to the symmetrical 5 KF intermediate prior to its conversion to pentose. When the mutant was grown on [1-³H]fructose in the presence of unlabeled 5 KF, [5-³H]fructose appeared in the culture medium. Thus, 5 KF served as the oxidant for the nicotinamide adenine dinucleotide phosphate, reduced form, generated during growth on fructose.

¹ Present address: Department of Microbiology, Mount Sinai School of Medicine, New York, N.Y. 10029.

² Present address: Department of Biochemistry, College of Medicine and Dentistry of New Jersey, Rutgers Medical School, Piscataway, N.J. 08854.