Effects of Adenine Nucleotides on Hydrogen-Ion Transport in Chloroplasts

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Abstract
1-10 muM ATP stimulated H(+) uptake and slowed the release of H(+) in the dark in chloroplasts illuminated at pH values at which photophosphorylation can occur, but not at pH 6.5. This ATP stimulation of H(+) uptake was abolished by an antiserum to the chloroplast coupling factor and was reduced by the energy transfer inhibitors phlorizin and Dio-9. ATP synthesis after illumination was also enhanced by ATP. Electron flow from water to methyl viologen was inhibited by the same low concentrations of ATP.ADP also increased the extent of H(+) uptake in chloroplasts, even in the presence of arsenate and MgCl(2). In the presence of hexokinase and glucose, as well as arsenate and Mg(++), ADP inhibited H(+) uptake. The failure of previous investigators to observe a direct inhibition of H(+) uptake by phosphorylation was probably caused by a masking of the inhibition by the stimulation of H(+) uptake by ATP. Furthermore, the stimulation of H(+) uptake by ATP provides an explanation for its inhibition of electron flow.