Studies on sodium-potassium-activated adenosinetriphosphatase. V. Correlation of enzyme activity with cation flux in six tissues

Abstract

The activity of the enzyme Na-K-activated ATPase, which is closely related to the active transport system of sodium and potassium in human erythrocytes, was determined in human erythrocytes, frog toe muscle, squid giant axone, frog skin, toad bladder, and in the noninnervated membrane of the Sachs organ of the electric eel. The temperature coefficient of the enzyme was determined in each tissue except the erythrocytes. The results were expressed in moles/sq. cm./sec. and compared with the active cation fluxes, expressed in the same units, for these tissues reported by other investigators. The enzyme activities were corrected for the temperature, at which the flux values had been obtained. A significant correlation was found between Na-K-activated ATPase activity and active cation flux over a 25,000-fold range. The average ratio of equivalents cation transported per mole ATP hydrolyzed (cation/ATP ratio) was 2.56 ± 0.19, which is significantly higher than 2, but not significantly different from 3. The total ATPase activity was not significantly correlated with the flux values. The value of 2.56 for the cation/ATP ratio agrees with many other determinations of this ratio for various tissues reported in the literature. These findings further strengthen the assumption that the Na-K-activated ATPase is closely related to the active cation transport involved in maintenance of ion gradients in single cells, transport of salt and water across epithelial membranes, and repolarization processes in muscle, nerve, and electric organs.