Question

In muscle cells, high energy charge [inhibits or "activates]  glycolysis. Specifically, ATP ["inhibits or activates"] the enzymes phosphofructokinase 1 and pyruvate kinase. The enzyme [hexokinase" or glucokinase] is negatively affected because of a build-up of [glucose 6-phosphate or fructose 1,6-bisphosphate]         .

Choose one of the answers in the brackets.

Answer 1

In muscle cells, high energy charge [inhibits]  glycolysis. Specifically, ATP ["inhibits] the enzymes phosphofructokinase 1 and pyruvate kinase. The enzyme [hexokinase"] is negatively affected because of a build-up of [glucose 6-phosphate]   

(High ATP/ADP ratio) indicates the energy of the cell. If there is high ATP concentration there is no need to oxidize glucose for the ATP production. So high energy charge inhibits glycolysis. Phosphofructokinase is a main regulatory and allosteric enzyme of glycolysis which is inhibited by the ATP. Glycolysis is regulated at three steps,

Glucose ----->glucose 6 phosphates (hexokinase/glucokinase)

Fructose 6 phosphate ------> fructose 1,6 bis phosphate (PFK-1)

Phosphoenolpyruvate -------> pyruvate (pyruvate kinase)

PFK and pyruvate kinase are inhibited by ATP and activated by ADP.

Inactivation of the PFK leads to the accumulation of glucose 6 phosphate (present in equilibrium with fructose 6 phosphate). Elevated level of glucose 6 phosphate inhibits hexokinase enzyme.