PHOSPHOFRUCTOKINASE

PFK

http://oregonstate.edu/instruct/bb450/fall2011/stryer7/16/figure_16_16.jpg

Glycolysis

Phosphofructokinase catalyses the third reaction of glycolysis

The reverse reaction in Gluconeogenesis is catalyzed by fructose-1,6-bisphosphatase

Regulation of glycolysis

These reactions are all kinases: catalysis of reactions involving the addition or removal of phosphate groups

Reaction 1 – HexokinaseReaction 3 – PFKReaction 10 – Pyruvate kinase

Voet, Voet, Pratt 4th Ed. Fig 15-21

There are three largely negative ΔG reactions in glycolysis which are used to mediate flux

Why PFK is the major flux mediator

The hexokinase step is often bypassed as all glucose-1-phosphate created from glycogenolysis can be converted directly to glucose-6-phosphate via phosphoglucomutase enzyme.

The pyruvate kinase reaction is the last one and therefore is not used to mediate glycolysis directly, it is used to mediate the overall metabolism of metabolites.

Voet, Voet, Pratt 4th edition fig 16-5

Structure of PFK

Is regulated by allosteric ligands that alter the binding of the substrate

Phosphofructokinase is a homotetramer that displays allostery.

Has two unique dimer-dimer interfaces1) Four substrate-binding interfaces2) Four effector –binding interfaces

Allosteric interactions

Allosteric inhibition Phosphoenolpyruvat

e ATP

Allosteric activation ADP AMP Fructose-2,6-

bisphosphate At low metabolic demand, ATP concentrations are high, ADP and

AMP concentrations are low and there PFK is allosterically inhibited. Conversely, during exercise when ATP concentrations decrease subsequently increasing the concentrations of ADP and AMP, PFK in allosterically activated to promote the uptake of metabolites and the production of ATP

Pyruvate kinase indirectly regulates metabolic flux through glycolysis by inhibiting PFK with the build up of phosphoenolpyruvate.

PFK-2 can be targeted to increase F2,6P concentrations in order to allosterically activate PFK when there is a metabolic demand.

http://oregonstate.edu/instruct/bb450/fall2011/stryer7/16/figure_16_17.jpg

At low levels of ATP the forward reaction is much more favorable. In vivo studies show that low [ATP] account for <10% increase in metabolic flux however PFK activity can change 100-fold. This is accounted for the preferential binding of AMP and ADP to the R-state.