title: An analysis of some thermodynamic properties of iron-sulphur centres in site I of mitochondria.
abstract: 1. The midpoint potentials of the various iron-sulphur centres in Site I were determined at different pH values by the technique of redox potentiometry. An interesting feature is the pH-dependence of Centre N-2, the highest potential component of the NADH dehydrogenase segment of the respiratory chain. 2. The apparent midpoint potentials of Centre N-2 (NADH dehydrogenase) and S-1 (succinate dehydrogenase) and their pH-dependence was also determined by using the succinate/fumarate couple. Again Centre N-2 is pH-dependent in midpoint potential, and Centre S-1 is not. The results obtained by titrating with the succinate/fumarate couple are in quantitative agreement with those obtained for these centres by redox potentiometry. 3. Oxidation-reduction titrations of iron-sulphur centres with the couple NADH/NAD+ and an analogue APADH/APAD+ in the presence of rotenone gave results substantially different from those obtained by redox potentiometry; these differences may be due to the mechanism of action of NADH dehydrogenase and its specific interaction with NADH. 5. The addition of ATP to an NAD+/NADH-poised system induces an uncoupler-sensitive oxidation of Centre N-4.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D008564:Membrane Potentials; D008667:Metalloproteins / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000378:metabolism*; D009243:NAD / Q000031:analogs & derivatives; D010084:Oxidation-Reduction; D011199:Potentiometry; D013816:Thermodynamics
chemical_list: D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D009243:NAD; C005941:3-acetylpyridine adenine dinucleotide; D000255:Adenosine Triphosphate