PMID: 1648963Jul 16, 1991

Dependence of kinetic parameters of chloroplast ATP synthase on external pH, internal pH, and delta pH

Biochemistry
T BizouarnF Haraux

Abstract

ATP synthesis by the membrane-bound chloroplast ATPase in the oxidized state of its gamma disulfide bridge was studied as a function of the ADP concentration, delta pH, and external pH values, under conditions where delta pH was clamped and delocalized. At a given pH, the rate of phosphorylation at saturating ADP concentration (Vmax) and the Michaelis constant Km (ADP) depend strictly on delta pH, irrespective of the way the delta pH is generated: there evidently is no specific interaction between the redox carriers and the ATPase. It was also shown that both Km (ADP) and Vmax depend on delta pH, not on the external or internal pH. This suggests that internal proton binding and external proton release are concerted, so that net proton translocation is an elementary step of the phosphorylation process. These results appear to be consistent with a modified "proton substrate" model, provided the delta G0 of the condensation reaction within the catalytic site is low. At least one additional assumption, such as a shift in the pK of bound phosphate or the existence of an additional group transferring protons from or to reactants, is nevertheless required to account for the strict delta pH dependence of the rate of ATP synthesis. A pu...Continue Reading

References

Sep 11, 1979·Biochimica Et Biophysica Acta·J D Mills, G Hind
Nov 13, 1990·European Journal of Biochemistry·H StrotmannW Baum
Feb 1, 1985·Archives of Biochemistry and Biophysics·A LoehrB Huchzermeyer
Jun 1, 1986·Proceedings of the National Academy of Sciences of the United States of America·G A Scarborough
Oct 1, 1974·The Journal of Cell Biology·M P Garber, P L Steponkus
May 25, 1972·Biochimica Et Biophysica Acta·J Rosing, E C Slater
Oct 1, 1973·Proceedings of the National Academy of Sciences of the United States of America·P D BoyerW Momsen
Apr 30, 1981·Biochemical and Biophysical Research Communications·C Vinkler
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Related Concepts

Magnesium ADP
Etioplasts
H(+)-Transporting ATP Synthase, Acyl-Phosphate-Linked
Hydrogen-Ion Concentration
Oxidation-Reduction
Phosphorylation
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Protons
Substrate Specificity
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