Abstract
1. A study has been made of the chemical reactions associated with the active transport of sodium and potassium in human red cells, with special reference to the action of oligomycin and the labelling of cell membranes by radioactive ATP.2. Oligomycin had the same effects as ouabain on the various aspects of active transport in red cells. It inhibited sodium and potassium transport, the transport ATPase, and the lactate production that is controlled by the sodium pump.3. When cell membranes were incubated with radioactive ATP they became labelled. The labelling, however, was unrelated to the activity of the transport ATPase. Incubation of membranes and intact cells showed that the labelling was a result of physical adsorption of inorganic phosphate to the membranes.4. The results show that if there is a phosphate intermediate in the reaction of the transport ATPase in human red cell membranes, then it is present in amounts too small to be detectable by the methods that have been successfully used with organs such as brain and kidney.