Premium
Kinetics and Thermodynamics of Oxidative Phosphorylation under Conditions that are Far from Thermodynamic Equilibrium
Author(s) -
Reynafarje Baltazar Davila
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a892-b
Subject(s) - oxidative phosphorylation , chemistry , chemiosmosis , protonation , redox , electron transport chain , adenosine triphosphate , uncoupling agents , atp synthase , bioenergetics , stoichiometry , kinetics , biophysics , steady state (chemistry) , membrane , mitochondrion , biochemistry , enzyme , inorganic chemistry , organic chemistry , biology , physics , ion , quantum mechanics
Resembling conditions existing in vivo, initial rates of O 2 utilization and ATP synthesis were simultaneously determined in reactions catalyzed by mitochondria and homogenates of whole tissues exposed to limiting concentrations of O 2 and ADP. The following novel aspects of the process of oxidative phosphorylation were found. 1) The actual rates of ATP synthesis are orders of magnitude higher than those observed under optimal State 3 metabolic conditions, but perfectly compatible with the very fast rates of electron flow and O 2 uptake. 2) The H + /O and ATP/O ratios, i.e. the number of H + ejected and molecules of ATP formed per atom of O 2 consumed are not constants but vary exquisitely depending on the Δ E h , the extent and state of reduction and/or protonation of the membrane, and the relative concentrations of O 2 and ADP. 3) The extent of ATP synthesis is neither kinetically nor thermodynamically related to the consumption of O 2 that occurs in State 3 under conditions in which the redox state of the membrane is mostly oxidized. 4) The ATP/O stoichiometry cannot be evaluated by only considering the amounts of ADP added and O 2 consumed in State 3. 5) The energy required for ATP synthesis comes not from the chemical component (ΔpH) of the protonmotive force (Δ p ) but from abrupt transitions in the structural and redox state of the membrane imposed by the electrical component (ΔΨ) of the Δ p . It is concluded that the mechanism of oxidative phosphorylation and ATP synthesis is electro‐mechanical rather than electro chemical or chemiosmotic.