1. 1. Studies of purified 6-phosphofructo-1-kinase (PFK) from white skeletal muscle of the rainbow trout (Oncorhynchus my kiss) were undertaken to illuminate aspects of the regulation of glycolysis in muscle under resting versus exercising conditions. 2. 2. Trout muscle PFK was strongly inhibited by ATP at physiological levels and was regulated by a number of allosteric effectors. 3. 3. Allosteric activators included ammonium ion, inorganic phosphate, AMP, ADP, and fructose-2,6-bisphosphate (F2.6P2); these enhanced enzyme affinity for F6P and reversed inhibition by ATP. 4. 4. Changes in pH also played a major role in PFK regulation; as pH decreased from 7.2 to 6.6 (mimicking the pH decrease during exhaustive exercise), not only was enzyme activity reduced, but the reaction cooperativity increased as well. 5. 5. The negative effect of reduced pH, however, was fully compensated for by the rise in the levels of positive modulators, such AMP following exercise. 6. 6. When assayed under substrate and effector concentrations that reflected "resting" vs "exercised" situations in muscle, the S0.5 values for F6P were reduced by 50- and 123-fold, respectively, to values of 0.068 and 0.15 mM, both close to the physiological levels of F6P.

International Journal of Biochemistry
Department of Biology

Su, J.Y. (Jeffrey Y.), & Storey, K. (1994). Regulation of rainbow trout white muscle phosphofructokinase during exercise. International Journal of Biochemistry, 26(4), 519–528. doi:10.1016/0020-711X(94)90009-4