Effect of temperature on the pH dependence of renal microsomal ATPase in the rabbit, rat and hamster.

The effects of temperature on the optimum pH of the renal microsomal Na-K-ATPase were studied in the rabbit, rat and hamster. The pH optimum of the ATPase in all three animals varied inversely with temperature, while a constant optimal OH-/H+ ratios were preserved at all temperatures. There appeared to be no difference between the Na-K-ATPase of the hibernating and non-hibernating representatives in terms of temperature dependence or substrate affinity. The pH optimum for the K-pNPPase activity was independent of temperature, indicating that the dephosphorylation step of Na-K-ATPase catalyzed reactions is not the source of the temperature dependence. These results are consistent with the Imidazole alphastat hypothesis of Reeves, which predicts that the optimal activity of the enzyme would occur at a constant pH-pKIM and thus a constant OH-/H+ ratio.