Question

How does allosteric modulation regulate glycolysis, gluconeogenesis, and glycogen levels?

Answer 1

1. The rate at which the glycolytic pathway operates is controlled primarily by allosteric regulation of three enzymes : Hexokinase , phosphofructokinase and pyruvate kinase. The reaction catalysed by these enzymes are irreversible. A high AMP concentration activates phosphofructokinase and pyruvate kinase. In contrast , a high ATP concentration inhibit both enzymes. Other allosteric effectors include fructose-6- phosphate which stimulates phosphofructokinase activity and glucose-6-phosphate , which inhibit the Hexokinase. Finally fructose-2,6- bisphosphate stimulate glycolysis by activating phosphofructokinase and fructose-1,6-bisphosphate activate pyruvate kinase.

2. Gluconeogenesis is the synthesis of glucose from non carbohydrate precursors. During gluconeogenesis seven steps are catalysed by the same enzymes used in Glycolysis these are

(A) conversation of glucose to glucose-6-phosphate catalysed by Hexokinase.

(B) conversion of fructose-6-phosphate to fructose-1,6- bisphosphate.

(C) The conversion of phosphoenolpyruvate to pyruvate by pyruvate kinase.

3.Glycogen is synthesized from glucose 6- phosphate mainly in the muscles and liver which are produced by Hexokinase that is a allosteric enzyme.