Sir Hans Krebs has emphasized that whenever there is a critical interconversion of two metabolic intermediates at a rate-limiting step in a metabolic pathway or at a branching point between two pathways, nature provides opposing unidirectional enzymatic reactions; these reactions produce a degree of control far beyond that provided by mass action through the equilibrium across a single bidirectional enzymatic process. Simply put, maintenance of blood glucose is not just a function of the level of glucose-6-phosphate in liver but, rather, of the levels of glucose and glucose-6-phosphate, and of the activities of two essentially opposed and unidirectional enzyme-catalyzed reactions: . . .
George F. Cahill (Thu,) studied this question.