5-Keto-D-fructose

Yeast hexokinase was shown to catalyze the phosphorylation of 5-keto-o-fructose (D-fhreo-2,5-hexodiulose) in the presence of ATP.The product was identified as a monophosphate ester.A procedure for the preparation of this ester and some of its properties are described.Reduction of the monophosphate ester by the NADPH-5-keto-nfructose reductase from Gluconobacter cerinus yielded fructose l-phosphate.5-Keto-n-fructose (athree-2,5-hexodiulose) is produced by several strains of Acetobacter growing on D-frUCtoSe (l-3).The reduction of this diketohexose to n-fructose has been shown to be catalyzed by a specific NADPH-linked reductase isolated from Gluconobacter cerinus cells (4, 5).TJtilization of 5KF1 as a carbon source for the growth of G. cerinus could be attributed, at least in part, to this reaction.During a study of the utilization of 5K-F by extracts of fructose-grown cells of G. cerinus, it became evident that the presence of a kinase activity resulted in the phosphorylation of this hexose wit'h ATP.Subsequently, it was found t,hat 5KF is a subst,rat,e for yeast hexokinase with formation of 5KF-l-phosphate.2Some kinetic properties of this reaction system and the characterization of 5KF-P are presented in this paper.5KF-P was found to be a substrate for the G. cerinus NIZDPH-5KF reductase (5) and the product of reduction was identified as fructose-l-P. 1METHODSCrystalline yeast hexokinase and other purified enzymes used in this work were purchased from Boehringer und Soehne, GmbH