Interactions among pyruvate concentration, pH, and Km of pyruvate in determining in vivo Q10 values of the lactate dehydrogenase reaction

Abstract

The interactions among pyruvate concentration, the apparent Michaelis constant (K_m) of pyruvate, and intracellular pH on the Q₁₀ of the lactate dehydrogenase (LDH) reaction of white skeletal muscle of the fish Gillichthys mirabilis were studied. Experimentally determined values for pyruvate concentration and K_m of pyruvate (measured under both constant pH and variable (=biologically realistic) pH were used to estimate in vivo Q₁₀'s over acclimation time courses and in acute temperature-change situations. Temperature-dependent changes in pyruvate concentration were large. The 25 °C acclimated fish had approximately twice the pyruvate concentration of 15 °C acclimated specimens, and acute temperature changes also led to higher pyruvate levels at higher temperatures. These temperature-dependent changes in pyruvate concentration prevent temperature-dependent variation in the K_m of pyruvate from having Q₁₀-reducing influences. Rather, during acclimation a relatively stable ratio of K_m: [substrate] is maintained. This is viewed as important for the preservation of correct regulatory capacity for the muscle LDH reaction.