Mechanistic implications of the potassium‐potassium exchange carried out by the sodium‐potassium pump.

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Abstract
The magnitude of the K-K exchange carried out by the Na pump in human red cells was measured as a function of the external K concentration in cells with high and low intracellular K. The apparent K1/2 for external K and the Vm increased by the same proportion when intracellular K was raised. The K-K exchange is apparently part of a ping-pong reaction mechanism. The velocity of the exchange increases monotonically with intracellular phosphate and ATP concentration; neither substrate inhibits at very high concentration. The enzyme species which carries out the exchange apparently should be both phosphorylated and combined with ATP.