22. Phosphofructokinase is an allosteric enzyme that catalyzes the conversion of

Question

22. Phosphofructokinase is an allosteric enzyme that catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, an early step of glycolysis. An increased accumulation of ATP (an allosteric regulator of PFK) would be expected to... a inhibit the enzyme and slow the rates of glycolysis and the citric acid cycle. b activate the enzyme and slow the rates of glycolysis and the citric acid cycle. c. inhibit the enzyme and thus increase the rates of glycolysis and the citric acid cycle. d. activate the enzyme and increase the rates of glycolysis and the citric acid cycle. e. ATP would have no effect on the rates of glycolysis and the citric acid cycle.

Explanation / Answer

22. Ans . Option [c] inhibits the enzyme and increases the rate of glycolysis and citric acid cycle.

Reason- PFK is the most important control site in mammalian glycolytic pathway. It is inhibited by high ATP levels but AMP reverses the inhibitory action of ATP. Therefore the activity of the enzyme increases when ATP/AMP ratio is lowered. In other words, glycolysis is stimulated as the energy charge falls.

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