| Abstract: | Chitose-6-P (2,5-anhydromannose-6-P) induces ATPase activity of fructose-6-P kinase with a Vmax 2-3% that of the normal kinase reaction with fructose-6-P or 2,5-anhydromannitol. Chitose (and presumably also chitose-6-P) is 52% hydrated in water while chitose deuterated at C-1 is 60% hydrated because of the equilibrium isotope effect of 0.73 on aldehyde hydration. Deuterated chitose-6-P gave a normal isotope effect on V/K of 1.23, but no effect on Vmax, showing that the free aldehyde is the activator and the hydrated form does not bind appreciably. With fructokinase, chitose can act either as a substrate, being phosphorylated at C-6 when adsorbed with C-6 next to MgATP, or as an inducer of ATPase activity when adsorbed with C-1 next to MgATP. The ATPase has a rate about 25% that of the kinase. |
