The allosteric properties of rat liver fructose-1,6-bisphosphatase.
Inhibition of rat liver fructose-1,6-bisphosphatase by AMP was uncompetitive with respect to fructose 1,6-bisphosphate in the absence of fructose 2,6-bisphosphate, but non-competitive in its presence. AMP was unable to bind to the enzyme except in the presence of one of the fructose bisphosphates; the binding stoicheiometry was 2 molecules/tetramer. Increasing concentrations of Mg2+ increased the Hill coefficient h and the apparent Ki for AMP, whereas fructose 2,6-bisphosphate had the opposite effect. Increasing concentrations of both AMP and fructose 2,6-bisphosphate decreased h and increased the apparent Ka for Mg2+. AMP slightly decreased, and Mg2+ slightly increased, the apparent Ki for fructose 2,6-bisphosphate, but each had only small effects on h. These results are interpreted in terms of a new three-state model for the allosteric properties of the enzyme, in which fructose 2,6-bisphosphate can bind both to the catalytic site and to an allosteric site and AMP can bind to the enzyme only when the catalytic site is occupied.
D000249:Adenosine Monophosphate / Q000494:pharmacology; D000494:Allosteric Regulation; D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D006597:Fructose-Bisphosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005635:Fructosediphosphates / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008274:Magnesium / Q000494:pharmacology; D008954:Models, Biological; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains
D005635:Fructosediphosphates; D000249:Adenosine Monophosphate; C027652:fructose 2,6-diphosphate; D006597:Fructose-Bisphosphatase; D008274:Magnesium