Resolved difference spectra of redox centers involved in photosynthetic electron flow in Rhodopseudomonas capsulata and rhodopseudomonas sphaeroides |
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Authors: | John R Bowyer Steven W Meinhardt Gerrard V Tierney Antony R Crofts |
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Institution: | Department of Physiology and Biophysics, 524 Burrill Hall, University of Illinois, Urbana, IL 61801 U.S.A. |
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Abstract: | 1. In Rhodopseudomonas sphaeroides the Qx 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 (λmax at 551–551.25 nm); this position was always red-shifted in comparison to that of isolated cytochrome c2 (λmax 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 b50 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 b50 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. |
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Keywords: | Electron transfer Bacterial photosynthesis Cytochrome Reaction center Ubisemiquinone Difference spectrum (Rps sphaeroides Rps capsulata) Mops LDAO UHDBT reaction center bacteriochlorophyll dimer oxidised dimer primary acceptor ubiquinone secondary acceptor uniquinone extinction coefficient difference between reduced and oxidised forms the oxidation-reduction potential referred to the standard hydrogen electrode To whom correspondence should be addressed Current address: Department of Biochemistry and Biophysics School of Medicine G5 University of Pennsylvania Philadelphia PA 19104 U S A |
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