The incorporation of inorganic phosphate into adenosine triphosphate by reversal of the sodium pump

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Abstract
Resealed ghosts were prepared containing much K, very little Na, and ATP, ADP and 32p-labelled orthophosphate (Pi) at concentrations such that the ratio [ATP]/([ADP].[Pi]) was low. Iodoacetate, iodoacetamide or both were also presented. The ghosts were incubated in high Na, K-free media with and without ouabain, or in high-K media, and the incorporation of 32p into ATP and ADP in 15 min. was measured. There was some incorporation of 32p into the nucleotides whatever the medium, possibly because of the residual activity of glycolytic enzymes, but in every experiment there was extra incorporation when the ghosts were in a high Na, K-free medium. This extra incorporation was largely abolished by ouabain (5 experiments) and partly abolished by oligomycin (1 experiment). It seems that if conditions are such that the over-all reaction associated with transport ATPase activity leads to an increase in free energy, the transport system will run backwards at a measurable rate and ATP will be synthesized at the expense of energy derived from ionic concentration gradients. The nature of the transport system is discussed in the light of the findings of this paper and the 4 preceding papers.