The influence of ions on the labelling of adenosine triphosphate in red cell ghosts.

1. The ionic composition of human red cell ghosts and suspending Ringer solutions have been varied independently. Measurements were made of the incorporation of [(32)P]o-phosphate ((32)P(i)) into ATP associated with different concentration gradients of Na and K across the membrane.2. Some incorporation of (32)P(i) was always found irrespective of the ionic composition of ghosts or media. However, additional labelling of energy-rich phosphate occurred when low Na, high K ghosts were incubated in a high Na, K-free medium. This did not occur when there was only a gradient of either Na or K. Downhill movements of both Na into and K out of the ghosts were needed for the extra labelling.3. Even in the presence of suitable ionic gradients, the extra incorporation was prevented by ouabain or by adding a small amount of external K sufficient to facilitate normal operation of the Na pump.4. Increase in internal P(i) stimulated the incorporation.5. The results show that the conditions for forward and backward running of the ATPase system associated with the Na pump are such that both reactions cannot proceed optimally at the same time.