The Mechanism of 6-Deoxyhexose Synthesis

The enzyme system from Pseudomonas aeruginosa ATCC 7700 catalyzing the conversion of deoxythymidine diphosphate 4-keto-6-deoxy-d-glucose to deoxythymidine diphosphate-l-rhamnose, dTDP-4-keto-6-deoxy-d-glucose + TPNH + H+ → TPN + dTDP-l-rhamnose has been separated into two protein fractions. Both fractions are required for the over-all reaction. Enzyme II will catalyze the exchange of the hydrogens at C-3 and C-5 of dTDP-4-keto-6-deoxy-d-glucose with the medium. dTDP-l-rhamnose synthesized with the purified enzymes in D2O contains 1 atom of deuterium at C-3 and 1 atom of deuterium at C-5 of l-rhamnose. Possible mechanisms to account for these observations are discussed. These mechanisms postulate that dTDP-4-keto-6-deoxy-l-mannose bound to Enzyme II is reduced by Enzyme I and TPNH. Heat denaturation studies indicate that Enzyme I can bind TPNH.