The Na+, K+-ATPase activation energy of the embryos of a cold-blooded loach

Abstract

The Na + , K + -ATPase is an ubiquitously expressed P-type of ATPase. Its main role is to maintain Na + and K + gradients across the plasma membrane by ATP-driven active transport. The Na + , K + -ATPase was one of the first ion pumps studied because of its importance in main-taining osmotic and ionic balances between intracellular and extracellular environments. Ad-ditional extracellular stimuli have been shown to induce internalization of the Na in the incubation medium, including the loss of endogenous phosphorus Pi in the membrane preparation, expressed in μmoles Pi per minutes per milligram of protein. The amount of endogenous phosphorus has been identified by the modified Fiske-Subbarow method, the quanti-tation of protein in the membrane preparation has been determined by Lowry method and the activation energy – in the Arrhenius coordinates. The activity of ouabain-sensitive ATPase under the change in the incubation medium temperature gradually increased at the stages of embryos development by an average of 23.4 ± 1.6% as compared with the control group. The maximum value of the enzymatic activity of Na + , K + pump of the embryos has been defined at the 8-stage of blastomers division (270 min). At the 6th hour of the development, no significant changes in the activity of Na + , K + -ATPase has been observed in comparison with the previous stage of the development. The results have shown that with the temperature change (10 o C) of the incubation medium, the Na + , K + -ATPase activity increased significantly at the investigated stages of the development. For Na + , K + -ATPase, a nonlinear dependence of the enzymatic activity on the temperature in the Arrhenius coordinates was found; the activation energy is 10.6 ÷ 20.8 kJ / mol. The calculated values of the Na + , K + -ATPase activation energy of the loach embryos during embryogenesis are consistent with the existing data and are likely due to the binding strength of the investigated ATP-hydrolase to membrane lipids during the embryonal cell division.