EFFECTS OF AMP AND FRUCTOSE 2,6-BISPHOSPHATE ON FLUXES BETWEEN GLUCOSE-6-PHOSPHATE AND TRIOSE-PHOSPHATE IN RENAL CORTICAL EXTRACTS

Gluconeogenic flux exceeds glycolytic flux at the hexose-phosphate ste ps when measured in extracts of kidney cortex from well-fed rats. Addi tion of AMP and/or fructose 2,6-bisphosphate to the assay medium parti ally eradicates the difference. Using principles developed by Kacser, H., and Burns, J. A. ((1973) in Rate Control of Biological Processes ( Davies, D. D., ed) pp. 65-104, Cambridge University Press, London) and Heinrich R., and Rapoport T. A. ((1974) Eur. J. Biochem. 42, 97-105), flux control coefficients of enzymes participating in the pathway seg ments from glucose 6-phosphate to triose-phosphates and from glycerol 3-phosphate to glucose 6-phosphate were determined by additions of the respective enzyme to the system. Results show that the flux control c oefficients are highly modulated by the presence of allosteric effecto rs, as might be expected according to the regulatory properties of pho sphofructokinase and fructose-1, 6-bisphosphatase purified from this o rigin. Measured reductions of fructose 2,6-bisphosphate and AMP levels during acidosis, starvation, or after phenylephrine treatment suggest that these changes contribute to enhanced gluconeogenesis under these conditions.