Abstract
A 6PFK-lacking mutant of B. flavum grew on fructose but its FBPase-lacking mutant did not. The product of the PTS reaction from fructose as a substrate was not F6P but F1P. These indicate that fructose is metabolized through F1P. 1PFK and 6PFK which form F1, 6P2, an intermediate common to both glucose and fructose metabolism, were highly specific for their respective substrates, F1P and F6P. Both the reactions followed Michaelis-Menten kinetics. Kms of 1PFK for F1P and ATP were 0.6 and 0.18 mM, and those of 6PFK for F6P and ATP were 2.4 and 0.15 mM, respectively. Reaction mechanisms of 1PFK and 6PFK were of Ordered Bi Bi and of Ping Pong, respectively. 1PFK was inhibited by F6P and the reaction products, F1, 6P2 and ADP, with Kis of 0.9, 2.1, and 1.5 mM, respectively. 6PFK was inhibited only by ADP with a Ki of 0.45 mM, but was neither inhibited by ATP, citrate, and PEP nor activated by AMP and F2, 6P2. The inhibition of 1PFK by F6P and F1, 6P2 was competitive to F1P and of mixed type to ATP and that by ADP was of mixed type to both the substrates. The inhibition of 6PFK by ADP was uncompetitive to F6P and competitive to ATP, suggesting that ADP does not act as the reaction product but as an analog of the substrate, ATP.
