Describe the regulation of hexokinase/glucokinase, phosphofructokinase-1 (PFK-1)

Question

Describe the regulation of hexokinase/glucokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase in glycolysis

23: Compare and contrast the mechanisms for regulating glycolysis including allostery, hormonal regulation and covalent modification

24: Describe the regulation of hexokinase/glucokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase in glycolysis

24: Describe feed-forward activation (Module 1)

25: Provide examples of each of the following major classes of receptors and compare and contrast their mechanism of signaling and termination: receptor tyrosine kinases, serine/threonine linked receptors, G-Protein coupled receptors (heptahelical receptors), cytoplasmic/nuclear receptors and ion channel receptors

Explanation / Answer

The hexokinase is an allosteric enzyme which is inhibited by glucose-6-phosphate. Glucokinase is not inhibited by product as it is highly specific to D-glucose and has a higher Km for it. Glucokinase is an inducible enzyme and is regulated by insulin.

Phosphofructokinase-1 is regulated by ATP which acts as an inhibitor. When the level of ATP is high, the Km for fructose-6- phosphate is increased resulting in turning off of glycolysis. AMP, on the other hand, reverses the ATP’s inhibitory action. Phosphofructokinase-1 is also inhibited by citrate. Citrate inhibits the enzyme by elevating the inhibitory effect of ATP. Phosphofructokinase-1 is activated by D-fructose-2,6-bisphosphate by increasing the affinity for the substrate( fructose-6-phoshate) and decreasing the inhibitory effect of ATP. This enzyme is also controlled by pH. Decrease in pH causes inhibition which prevents excessive lactic acid formation and a drop in blood pH.

Pyruvate Kinase has allosteric sites for a number of effectors. It is activated by AMP and fructose-1,6-bisphosphate and inhibition is caused by ATP, acetyl-Co A and alanine. It is also regulated by covalent modification. Hormones like glucagon activate a c-AMP dependent protein kinase. The phosphorylated pyruvate kinase is strongly inhibited by ATP and alanine.

Tyrosine Kinases (phosphorylation): insulin receptor and jak-STAT

Serine- threonine kinase: TGF beta

G-protein coupled receptor(GPCR): glucagon and epinephrine receptor

Related Questions

Navigate

• Browse (All)
• Browse D
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.