Resolved difference spectra of redox centers involved in photosynthetic electron flow in Rhodopseudomonas capsulata and rhodopseudomonas sphaeroides

Abstract

1. In Rhodopseudomonas sphaeroides the Q x absorption band of the reaction center bacteriochlorophyll dimer which bleaches on photo-oxidation is both blue-shifted and has an increased extinction coefficient on solubilisation of the chromatophore membrane with lauryldimethylamine- N-oxide. These effects may be attributable in part to the particle flattening effect. 2. The difference spectrum of photo-oxidisable c type cytochrome in the chromatophore was found to have a slightly variable peak position in the α-band ( λ max at 551–551.25 nm); this position was always red-shifted in comparison to that of isolated cytochrome c 2 ( λ max at 549.5 ± 0.5 nm). The shift in wavelength maximum was not due to association with the reaction center protein. A possible heterogeneity in the c-type cytochromes of chromatophores is discussed. 3. Flash-induced difference spectra attributed to cytochrome b were resolved at several different redox potentials and in the presence and absence of antimycin. Under most conditions, one major component, cytochrome b 50 appeared to be involved. However, in some circumstances, reduction of a component with the spectral characteristics of cytochrome b −90 was observed. 4. Difference spectra attributed to (BChl) 2, Q ⨪ II, c type cytochrome and cytochrome b 50 were resolved in the Soret region for Rhodopseudomonas capsulata. 5. A computer-linked kinetic spectrophotometer for obtaining automatically the difference spectra of components functioning in photosynthetic electron transfer chains is described. The system incorporates a novel method for automatically adjusting and holding the photomultiplier supply voltage.