This enzyme maintains the balance of sodium and potassium ions in the living cell. Professor Skou made his pioneer work at the Department of Physiology, University of Aarhus, where Professor Skou was employed as an assistant professor in 1947 and from 1963 as a full professor until he in 1978 was nominated to become the professor of biophysics at this university without advertising the post. The influence of sodium, potassium, magnesium and calcium ions on this enzyme has been investigated. The presence of magnesium ions is an obligatory requirement for the activity of the enzyme.
Sodium ions increase the activity when magnesium ions are present.
Potassium ions increase the activity when the system contains both magnesium and sodium ions. Calcium ions inhibit the enzyme under all conditions. If potassium ions are added, the optimum magnesium concentration is doubled. If calcium ions are also added, the optimum magnesium concentration becomes still higher, and it increases with the calcium concentration. If the system contains the four cations in concentrations roughly equal to those in the crab-nerve axoplasm, an increase in the sodium concentration as well as a decrease in the potassium concentration will lead to an intensification of the enzyme activity.