Question 2. Phosphofructokinase1 The effect of ATP on the allosteric enzyme PFK-1 is shown below. For a give concentration of Fructose-6- phosphate, the PFK-1 activity increases with increasing concentrations of ATP, but a point is reached beyond which increasing the concentration of ATP inhibits the enzyme. a) Explain how ATP can be both a substrate and an inhibitor of PFK-1. How is the enzyme regulated by ATP? b) The inhibition of PFK-1 by ATP is diminished when the ADP concentration is high, as shown in the diagram. How can this observation be explained?
Question
Question 2. Phosphofructokinase1 The effect of ATP on the allosteric enzyme PFK-1 is shown below. For a give concentration of Fructose-6- phosphate, the PFK-1 activity increases with increasing concentrations of ATP, but a point is reached beyond which increasing the concentration of ATP inhibits the enzyme. a) Explain how ATP can be both a substrate and an inhibitor of PFK-1. How is the enzyme regulated by ATP? b) The inhibition of PFK-1 by ATP is diminished when the ADP concentration is high, as shown in the diagram. How can this observation be explained?
Solution
a) ATP acts as both a substrate and an inhibitor for the enzyme Phosphofructokinase-1 (PFK-1), which plays a crucial role in the regulation of glycolysis. As a substrate, ATP is required for the phosphorylation of Fructose-6-phosphate to Fructose-1,6-bisphosphate, a key step in the glycolytic pathway. However, when ATP levels are high, it also acts as an inhibitor. This is because PFK-1 has two different ATP binding sites - one is the active site where ATP is a substrate, and the other is a regulatory site where ATP acts as an inhibitor. When ATP binds to the regulatory site, it induces a conformational change in the enzyme, reducing its affinity for Fructose-6-phosphate and thus inhibiting the enzyme's activity. This is a form of feedback inhibition, where the end product of a pathway inhibits an enzyme that acts earlier in the pathway, preventing overproduction of the end product.
b) ADP, being a product of ATP hydrolysis, competes with ATP for the regulatory site on PFK-1. When ADP levels are high, more ADP binds to the regulatory site, preventing ATP from binding and inhibiting the enzyme. This allows PFK-1 activity to continue even when ATP concentrations are high. This mechanism ensures that glycolysis can continue to produce ATP when the cell's energy demand is high, despite the presence of high levels of ATP.
Similar Questions
What statements are TRUE? Phosphofructokinase (PFK) is:i) activated by elevated ATP/ADP ratiosii) activated by AMPiii) inhibited by AMPiv) requires fructose 6 phosphatev) a rate limiting enzyme of glycolysisvi) reversiblevii) the commitment step in glycolysisviii) requires ATP
PFK1 is a key enzyme in the mammalian glycolytic pathway. Discuss the effects of ATP, AMP, PEP and citrate on PFK1 activity and, therefore, on cellular metabolism more broadly (10 marks) Discuss the effects of fructose 2,6 bisphosphate on PFK1 activity and the significance of this regulation (5marks) Why is this step so heavily controlled? (5 marks)
Phosphofructokinase-1 converts Fructose 6-phosphate to Fructose 1,6- bisphosphate. Which statement about the reaction is CORRECT? Under anaerobic conditions, this reaction plays an important role in regenerating NAD+ for use in the “pay-off” phase of glycolysis. This reaction occurs in the cytoplasm and is performed by an enzyme shared between glycolysis and gluconeogenesis. This is a readily reversible reaction which is allosterically regulated by Fructose 1,6- bisphosphate. The bifunctional PFK-2/FBPase-2 enzyme controls the concentration of the allosteric regulator of this reaction.
Which of the following glycolytic enzymes requires ATP as a substrate?Group of answer choicesHexokinaseAldolaseEnolasePyruvate kinase
The first ATP forming reaction in glycolysis is catalysed by which enzyme?Group of answer choicesglyceraldehyde 3-phosphate dehydrogenasephosphofructokinase-1phosphoglycerate kinasehexokinase
Upgrade your grade with Knowee
Get personalized homework help. Review tough concepts in more detail, or go deeper into your topic by exploring other relevant questions.