Oxidation-reduction potential dependence of the interaction of cytochromes, bacteriochlorophyll and carotenoids at 77°K in chromatophores of Chromatium D and Rhodopseudomonas gelatinosa

Abstract

1. A technique for assay of light-induced reactions at 77°K as a function of oxidation-reduction potential has been developed. 2. The light-induced reactions at 77°K in Rhodopseudomonas gelatinosa and Chromatium D have been studied as a function of oxidation-reduction potential imposed on the chromatophores before freezing. 3. In Chromatium D, cytochrome C553 ( E m + 10 mV) is oxidized by the bacteriochlorophyll reaction center complex ( E m + 470 mV) which undergoes light-induced bleaching at 615 nm, 430 nm and 400 nm; these spectral components are probably part of the reaction center P890 (P883). The evidence suggests that either of two cytochrome C553 hemes are capable of transferring electrons to bacteriochlorophyll + at 77°K. The primary electron acceptor associated with the reaction center bacteriochlorophyll has E m −135 mV. 4. In R. gelatinosa, cytochromes C422 ( E m + 280 mV) and C419 ( E m + 128 mV) are both apparently oxidized by a reaction center bacteriochlorophyll, E m + 400 mV; the molar ratio of these three components reacting at 77°K is 0.55:1:1, respectively. The primary electron acceptor of this system has E m −140 mV. However, the fact that some cytochrome oxidation was detectable at −350 mV indicates another and lower potential acceptor. 5. Evidence in the cited species indicates that a single reaction center oxidizes both the high and low potential cytochromes. 6. As the ambient oxidation-reduction potential is decreased, the control of cytochrome C422 oxidation in R. gelatinosa appears directly associated with the oxidation-reduction curve of the low potential cytochrome C419. 7. Carotenoid absorbance changes observed in R. gelatinosa at 77°K appear to respond to the light-induced oxidation-reduction reactions of reaction center bacteriochlorophyll, the primary electron acceptor, and to the cytochromes; the carotenoid changes may result from electrostatic field alterations.