Bioquímica e Fisiologia: Acesso Aberto

Abstrato

The Electromechanical Mechanism of ATP Synthesis in the Presence of In Vivo Concentrations of Oxygen

Baltazar D Reynafarje

The synthesis of ATP is undoubtedly the most important phenomenon that occurs in living organisms. The following experimentally determined facts are mechanistically significant. 1) Net synthesis of ATP only occurs during the extremely fast respiratory process in which cytochrome aa3 undergoes net oxidation. 2) The hyperbolical processes of electron flow and O2 reduction to water precede the sigmoidal process of ATP synthesis. 3) The exergonic process of O2 consumption controls the level of ADP and the endergonic process of ATP synthesis, not vice versa. 4) The extent and rates of electron flow and O2 uptake are the same in the presence or absence of ADP. 5) The rates of O2 uptake and ATP synthesis are orders of magnitude higher in the presence of in vivo levels of O2 than under state-3 metabolic conditions in the presence ~230 μM O2. 6) The KM of cytochrome aa3 for O2 is close to 30 μM not below 0.5 μM. 7) The ATP/O ratio is not constant but changes from near zero to 3.4 exquisitely depending on the redox potential and the relative concentrations of cytochrome aa3, O2 and ADP. 8) Net ejection of H+ only occurs during the reduction of cytochrome aa3 and the slow phase of O2 uptake. It is concluded that the free energy responsible for the synthesis of ATP is not the protonmotive force but the structural changes that induced by the flow of electrons occur at the levels of cytochrome aa3 and ATP synthase.