THE EFFECT OF THERMAL ACCLIMATION AND EXERCISE UPON THE BINDING OF GLYCOLYTIC ENZYMES IN MUSCLE OF THE GOLDFISH CARASSIUS AURATUS

To examine whether the changes in metabolic organization induced by thermal acclimation modify glycolytic enzyme-binding, we acclimated goldfish, Carassiu auratus, to 8 and 25 ˚C and measured the binding of phosphofructokinase (PFK), aldolase, pyruvate kinase and lactate dehydrogenase to subcellular particles in red and white muscle. When fish were sampled at rest at their acclimation temperature, only the percentage binding of PFK in red muscle was altered by thermal acclimation. By contrast, exhausting exercise at 15 ˚C led to markedly higher levels of binding of PFK in muscle of warm- than of cold-acclimated fish. This pattern was apparent in both red and white muscle. The specific activity of PFK in red muscle declined with exhausting exercise in warm- but not in cold-acclimated fish. In contrast, the units of PFK bound per gram of muscle did not differ in exhausted warm- and cold-acclimated fish. Cold- and warm-acclimated fish did not differ in their accumulation of lactate in white muscle at exhaustion. Furthermore, the PFK from white muscle of warm- and cold-acclimated fish did not differ in the pH dependence of binding to subcellular particles. These changes in the dynamics of PFK binding with temperature acclimation suggest that soluble PFK may be more susceptible to exercise-induced inhibition in warm- than in cold-acclimated goldfish. While the percentage binding and the specific activity of the other glycolytic enzymes were little affected by exhausting exercise, the units of aldolase bound per gram of white muscle decreased with exercise in warm-acclimated fish