REGULATION OF RAINBOW-TROUT WHITE MUSCLE PHOSPHOFRUCTOKINASE DURING EXERCISE

1. Studies of purified 6-phosphofructo-1-kinase (PFK) from white skele tal muscle of the rainbow trout (Oncorhynchus mykiss) were undertaken to illuminate aspects of the regulation of glycolysis in muscle under resting versus exercising conditions. 2. Trout muscle PFK was strongly inhibited by ATP at physiological levels and was regulated by a numbe r of allosteric effecters. 3. Allosteric activators included ammonium ion, inorganic phosphate, AMP, ADP, and fructose-2,6-bisphosphate (F2, 6P(2)); these enhanced enzyme affinity for F6P and reversed inhibition by ATP. 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 exha ustive exercise), not only was enzyme activity reduced, but the reacti on cooperativity increased as well. 5. The negative effect of reduced pH, however, was fully compensated for by the rise in the levels of po sitive modulators, such AMP following exercise. 6. When assayed under substrate and effector concentrations that reflected ''resting'' vs '' exercised'' situations in muscle, the S-0.5 values for F6P were reduce d by 50- and 123-fold, respectively, to values of 0.068 and 0.15 mM, b oth close to the physiological levels of F6P.