The link between metabolism and active transport of sodium in human red cell ghosts
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Reconstituted human red blood cell ghosts have been used to assay various metabolic intermediates for their role in driving the Na∶K pump. ATP was identified as the primary substrate of the pump. The main evidence was based on 1) the finding that the only requirement for activation of the pump was the presence of ATP, whether incorporated directly or generated by an ATP-yielding reaction; 2) the discriminating effects of various metabolic inhibitors; 3) the competition between the pump and the hexokinase reaction for ATP; and 4) the difference in effects of adenosine and inosine in activating the pump in energy-depleted ghosts. ADP was found to affect the Na∶K pump due to the presence of an adenylate kinase and perhaps because of an effect on the phosphoryl potential. The sidedness of action of the cardiotonic steroid, strophanthidin, was evaluated and found to inhibit the Na∶K pump only from the outside of the membrane. Inhibition of the pump by strophanthidin was also found to spare ATP in reconstituted ghosts provided the nonspecific phosphatase activity was suppressed.
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