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 sedohe ptulose 7-phosphate and sedoheptulose 1,7-bisphosphate in rat liver cy tosol fractions was studied by means of phosphorus magnetic resonance spectroscopy. When the activity of 6-phosphofructo-1-kinase was inhibi ted by a high concentration of ATP, the addition of fructose 2,6-bisph osphate led to a marked decrease in sedoheptulose 7-phosphate levels, accompanied by an increased concentration of ADP. Fructose 2,6-bisphos phate essentially inhibited both the decrease in sedoheptulose 1,7-bis phosphate 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 reversible ar row sedoheptulose 1,7-bisphosphate in the liver, and thus control the flux through the nonoxidative stage of the pentose phosphate pathway.