Dissociation of phosphate from beef heart mitochondrial F1-ATPase. Effect of adenine nucleotides.

The effect of exposure to adenine nucleotides on the dissociation of phosphate bound to beef heart mitochondrial F1-ATPase (F1) has been studied using a layered Sephadex centrifuge column method. The order of effectiveness of nucleotides in facilitating Pi dissociation from F1 was ATP greater than AMP-PNP much greater than ADP (where AMP-PNP indicates adenosine 5'-(beta,gamma-imido)triphosphate) when phosphate had bound to F1 as Pi from the medium. When ATP was present in amounts substoichiometric to F1, essentially all of the ATP present bound to F1, and the molar ratio of Pi released to ATP bound was near one. Under similar conditions AMP-PNP bound equally well to F1, but in order to effect similar amounts of Pi release it was necessary to use approximately 10 times as much AMP-PNP as ATP. The order of effectiveness of nucleotides in facilitating dissociation of phosphate which had bound to F1 as the gamma-phosphate of ATP was ATP = AMP-PNP much greater than ADP. In this case ATP and AMP-PNP were as effective in facilitating phosphate dissociation as was ATP in the case in which phosphate had bound to F1 as Pi. It is concluded that when phosphate has bound to F1 as Pi, binding of one molecule of ATP or more than one molecule of AMP-PNP are sufficient to facilitate dissociation of phosphate. When phosphate has bound to F1 as the gamma-phosphate of ATP, binding of one molecule of either ATP or AMP-PNP is sufficient to facilitate dissociation of phosphate.