[Theoretical evidence for the need to suppress parasitic recirculation in the futile cycle fructose-6-P--fructose-1,6-P2]

Abstract

In connection with the discussion of a possible role of the futile cycle fructose-6-P in equilibrium or formed from fructose-1,6,-P2 in the regulation of the carbohydrate energy metabolism, simple stoichiometric models of glycolysis and gluconeogenesis are examined which take account of substrate recirculation in the cycle. The recirculation is shown to involve wasteful expenditure of ATP and to divert fructose-1,6-P2 from glycolytic phosphorylation ADP and fructose-6-P from glucose or glycogen resynthesis. As a result, the glycolytic system loses its capacity to stabilize the level of ATP, while gluconeogenesis proves to be not efficient. From the analysis performed it is concluded that normal energy metabolism should involve allosteric regulatory mechanisms to suppress substrate recirculation in the cycle.