Species difference in temperature dependence of cardiac (Na+ + K+)-ATPase activity

Cardiac (Na+ + K+)-ATPase from several species of animals were comparatively studied with respect to their molecular form and temperature dependence. The molecular weight of the catalytic subunit varied a little among species, but the difference did not correlate with the sensitivity of the enzyme to ouabain inhibition. Analysis of Arrhenius plots of the activities of the enzymes showed that enzymes showing break points of 24-25 degrees were relatively insensitive to ouabain inhibition whereas those enzymes with break points of 29-31 degrees were much more sensitive to the glycoside. This suggests that there is a difference in the interaction of cardiac (Na+ + K+)-ATPase with lipids between the ouabain-sensitive and -insensitive animals.