Theory of iron-sulfur center N-2 oxidation and reduction by ATP

Abstract

The data of Ohnishi (1975) and of Gutman and coworkers on iron-sulfur center N-2 in mitochondria and submitochondrial particles are examined in as much quantitative detail as possible from the standpoint of both chemiosmotic theory and of chemical intermediate (transductase) theory. A method of examination of the behavior of an energy transduction site by plotting its properties as a function of both the high and low redox potentials on either side of the site is described in some detail. That adding ATP causes center N-2 to go oxidized when buffered redox-wise on the low potential side and reduced when buffered on the high potential side can be explained by both chemiosmotic and chemical intermediate theory. Chemiosmotic explanations consistent with the data exclude location of N-2 at the inside of the mitochondrial membrane, but location at the out side or the middle or mobile across the membrane cannot be ruled out by present data. All four abridged transductase models of chemical intermediate theory can be fitted to the data by choice of parameters. That center N-2 is a simple redox couple located at either side of energy transduction site 1 is ruled out. Further experiments needed to clarify present ambiguities are shown to be: (i) Adding ATP while buffering (redox-wise) the NAD +-NADH inside whole mitochondria; (ii) mapping the apparent midpoint potential or, alternatively, the redox state as a complete function of the redox potentials on both the high and low sides; (iii) determination of differences that may be caused by sidedness of the preparation (mitochondria or submitochondrial particles); and (iv) determining effects of changing the partitioning of the proton motive force between ΔpH and membrane potential.