The effect of natural and synthetic D-fructose 2,6-bisphosphate on the regulatory kinetic properties of liver and muscle phosphofructokinases.
The effect of natural "activation factor" and synthetic fructose-2,6-P2 on the allosteric kinetic properties of liver and muscle phosphofructokinases was investigated. Both synthetic and natural fructose-2,6-P2 show identical effects on the allosteric kinetic properties of both enzymes. Fructose-2,6-P2 counteracts inhibition by ATP and citrate and decreases the Km for fructose-6-P. This fructose ester also acts synergistically with AMP in releasing ATP inhibition. The Km values of liver and muscle phosphofructokinase for fructose-2,6-P2 in the presence of 1.25 mM ATP are 12 milliunits/ml (or 24 nM) and 5 milliunits/ml (or 10 nM), respectively. At near physiological concentrations of ATP (3 mM) and fructose-6-P (0.2 mM), however, the Km values for fructose-2,6-P2 are increased to 12 microM and 0.8 microM for liver and muscle enzymes, respectively. Thus, fructose-2,6-P2 is the most potent activator of the enzyme compared to other known activators such as fructose-1,6-P2. The rates of the reaction catalyzed by the enzymes under the above conditions are nonlinear: the rates decelerate in the absence or in the presence of lower concentrations of fructose-2,6-P2, but the rates become linear in the presence of higher concentrations of fructose-2,6-P2. Fructose-2,6-P2 also protects phosphofructokinase against inactivation by heat. Fructose-2,6-P2, therefore, may be the most important allosteric effector in regulation of phosphofructokinase in liver as well as in other tissues.
D000249:Adenosine Monophosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000494:Allosteric Regulation; D000818:Animals; D002951:Citrates / Q000378:metabolism; D004789:Enzyme Activation; D005635:Fructosediphosphates / Q000494:pharmacology*; D006598:Hexosediphosphates / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D009132:Muscles / Q000201:enzymology*; D009928:Organ Specificity; D010732:Phosphofructokinase-1 / Q000378:metabolism*; D051381:Rats
D002951:Citrates; D005635:Fructosediphosphates; D006598:Hexosediphosphates; D000249:Adenosine Monophosphate; C027652:fructose 2,6-diphosphate; D000255:Adenosine Triphosphate; D010732:Phosphofructokinase-1