Cytochrome c2 and reaction center of Rhodospeudomonas spheroides Ga. membranes. Extinction coefficients, content, half-reduction potentials, kinetics and electric field alterations.

The reduced minus oxidized extinction coefficients (delta epsilon-red-ox) of reaction center P605 when in the chromatophore is about 20% smaller than in the detergent-isolated state. Presumably the coupling of the reaction center protein to the antenna bacteriochlorophylls and carotenoids causes this hypochromism. The chromatophore values for P605 are 19.5 mM- minus 1 times cm- minus 1 with the spectrophotometer on single beam mode at 605 nm, and 29.8 mM- minus 1 times cm- minus 1 on dual wavelength mode set at 605--540 nm. Cytochrome c2, which is not affected by detergent, has a delta epsilon-red-ox value at 550--540 nm of 19.0 mM- minus 1 times cm- minus 1.2. The total bacteriochlorophyll to reaction center bacteriochlorophyll protein (P) ratio is about 100: 1. The cytochrome c2: reaction center protein ratio approaches 2. In current French press chromatophore preparations, about 70% of the reaction centers are each associated on a rapid kinetic basis with two cytochrome c2 molecules (intact P-c2 units). The remaining reaction center proteins are not associated with cytochrome c2 on a kinetically viable bais and may be the result of damage incurred during mechanical rupture of the cells. 3...