H+/ATP ratio during ATP hydrolysis by mitochondria: modification of the chemiosmotic theory

Proc Natl Acad Sci U S A. 1977 May;74(5):1955-9. doi: 10.1073/pnas.74.5.1955.

Abstract

The stoichiometry of H+ ejection by mitochondria during hydrolysis of a small pulse of ATP (the H+/ATP ratio) has been reexamined in the light of our recent observation that the stoichiometry of H+ ejection during mitochondrial electron transport (the H+/site ratio) was previously underestimated. We show that earlier estimates of the H+/ATP ratio in intact mitochondria were based upon an invalid correction for scaler H+ production and describe a modified method for determination of this ratio which utilizes mersalyl or N-ethylmaleimide to prevent complicating transmembrane movements of phosphate and H+. This method gives a value for the H+/ATP ratio of 2.0 without the need for questionable corrections, compared with a value of 3.0 for the H+/site ratio also obtained by pulse methods. A modified version of the chemiosmotic theory is presented, in which 3 H+ are ejected per pair of electrons traversing each energy-conserving site of the respiratory chain. Of these, 2 H+ return to the matrix through the ATPase to form ATP from ADP and phosphate, and 1 H+ returns through the combined action of the phosphate and adenine nucleotide exchange carriers of the inner membrane to allow the energy-requiring influx of Pi and ADP3- and efflux of ATP4-. Thus, up to one-third of the energy input into synthesis of extramitochondrial ATP may be required for transport work. Since other methods suggest that the H+/site significantly exceeds 3.0, an alternative possibility is that 4 h+ are ejected per site, followed by return of 3 H+ through the ATPase and 1 H+ through the operation of the proton-coupled membrane transport systems.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenine Nucleotides / metabolism
  • Adenosine Triphosphatases / metabolism
  • Adenosine Triphosphate / metabolism*
  • Animals
  • Biological Transport, Active / drug effects
  • Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / pharmacology
  • Cations, Monovalent
  • Ethylmaleimide / pharmacology
  • Hydrogen / metabolism*
  • Hydrogen-Ion Concentration
  • Mitochondria, Liver / metabolism*
  • Models, Biological
  • Osmolar Concentration
  • Oxidative Phosphorylation / drug effects
  • Phosphates / metabolism
  • Rats

Substances

  • Adenine Nucleotides
  • Cations, Monovalent
  • Phosphates
  • Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone
  • Hydrogen
  • Adenosine Triphosphate
  • Adenosine Triphosphatases
  • Ethylmaleimide