The involvement of fructose 2,6-bisphosphate in substrate cycle control in the nonoxidative stage of the pentose phosphate pathway. A phosphorus magnetic resonance spectroscopy study

The role of fructose 2,6-bisphosphate in the interconversion of sedoheptulose 7-phosphate and sedoheptulose 1,7-bisphosphate in rat liver cytosol fractions was studied by means of phosphorus magnetic resonance spectroscopy. When the activit of 6-phosphofructo-1-kinase was inhibited by a high concentration of ATP, the addition of fructose 2,6-bisphosphate led to a marked decrease in sedopheptulsoe 7-phosphate levels, accompanied by an increased concentration of ADP. Frructose 2,6-bisphosphate essentially inhibited both the decrease in sedoheptulose 1,7-disphosphate concentration and the accumulation of P_i in the incubation mixture. The data provided evidence that fructose 2,6-bisphosphate can regulate the substrate cycle; sedoheptulose 7-phosphate sedoheptulose 1,7-bisphosphate in the liver, and thus control the flux through the nonoxidative stage of the pentose phosphate pathway.