PFK-Worksheet - worksheet from tutorial PDF

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All About Phosphofructokinase Phosphofructokinase (PFK) is an enzyme in the _______ pathway that catalyses the ATP dependent phosphorylation reaction to convert Fructose-6-Phosphate (F6P) into _______________ and ______. It is one of the key ____________ enzymes of the pathway. PFK is able to regulate glycolysis through allosteric _________. Allosteric ________ is a process by which a regulatory molecule binds to an enzyme at a site that is not the ______ site for another molecule. This causes a conformational change in the _____ site for the second molecule, preventing binding. PFK has two conformations, which are known as the _______ (t) and relaxed (r) state. When PFK is in the R state, it has a high affinity for its substrate, F6P. When PFK switches to the ___ state, its affinity for F6P decreases and its activity level drops off. The switching between states is triggered by metabolites which are related to the glycolytic pathway. In 1980, fructose 2,6-bisphosphate (F-2,6-BP) was identified as a potent ______ of phosphofructokinase. Fructose 2,6-bisphosphate activates PFK by increasing its affinity for F6P and diminishing the inhibitory effect of ATP. In essence, Fructose 2,6-bisphosphate is an allosteric activator that shifts the conformation of this enzyme from the T state to the R state. Phosphofructokinase-2

Figure 16.20Control of the Synthesis and Degradation of Fructose 2,6-Bisphosphate A low blood-glucose level as signaled by glucagon leads to the phosphorylation of the bifunctional enzyme and hence to a lower level of fructose 2,6-bisphosphate, slowing glycolysis. High levels of fructose 6-phosphate accelerate the formation of fructose 2,6-bisphosphate by facilitating the dephosphorylation of the bifunctional enzyme. Biochemistry. 5th Edition. Berg JM, Tymoczko JL, Stryer L. Section 16.2 ‘The Glycolytic Pathway Is Tightly Controlled’ http://www.ncbi.nlm.nih.gov/books/NBK22395/

Fructose 2,6-bisphosphate is formed in a reaction catalyzed by phosphofructokinase 2 (PFK2), a different enzyme from phosphofructokinase. Fructose 2,6-bisphosphate is hydrolyzed to fructose 6-phosphate by a specific phosphatase, fructose bisphosphatase 2 (FBPase2).

In the liver, the concentration of F6P rises when blood-glucose concentration is _____, and the abundance of F6P accelerates the synthesis of F-2,6-BP. Hence, an abundance of F6P leads to a higher concentration of F-2,6-BP, which in turn stimulates phosphofructokinase. The activities of PFK2 and FBPase2 are reciprocally controlled by ____________. When glucose is scarce, a rise in the blood level of the hormone glucagon triggers a signal cascade leading to the phosphorylation of this enzyme by _________ A. This modification activates FBPase2 and inhibits PFK2, lowering the level of F-2,6-BP. On the other hand, when glucose levels are _______, the enzyme loses its attached phosphate group. This covalent modification activates PFK2 and inhibits FBPase2, raising the level of F-2,6-BP and accelerating glycolysis....