Identification of the pigment pool responsible for the flash-induced carotenoid band shift in Rhodopseudomonas sphaeroides chromatophores (original) (raw)
Related papers
Journal of Physical Chemistry B, 1998
Ultrafast fluorescence upconversion has been used to probe electronic excitation transfer within the B800-B820 light-harvesting antenna of Rhodopseudomonas acidophila strain 7050. Emission from the carotenoid S 2 band decays in 54 ( 8 fs, and the bacteriochlorophyll B820 Q y band rises in approximately 110 fs. The B820 Q y rise time is wavelength-dependent. Energy-transfer rates between the carotenoid and several neighboring bacteriochlorophyll are calculated. Coupling strengths are estimated through transition dipoletransition dipole, polarization, and higher-order Coulombic coupling along with a new transition density volume coupling calculation. Data are compared to calculated energy-transfer rates through the use of a four-state model representing direct carotenoid to B820 energy transfer. The carotenoid emission data bound the S 2 to Q x transfer time between 65 and 130 fs. The S 1 to Q y transfer is assumed to be mediated by polarization and Coulombic coupling rather than by exchange; the transfer time is estimated to be in the picosecond regime, consistent with fluorescence quantum yield data. † Present address:
The carotenoid band shift in reaction centers from Rhodopseudomonas sphaeroides
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1977
A specific carotenoid associated with reaction centers purified from Rhodopseudomonas sphaeroides shows an optical absorbance change in response to photochemical activity, at temperatures down to 35 K. The change corresponds to a bathechromic shift of 1 nm of each absorption band. The same change is induced by either chemical oxidation or photo-oxidation of reaction center bacteriochlorophyll (P-870). Reduction of the electron accepter of the reaction center, either chemically or photochemically, does not cause a carotenoid absorbance change or modify a change already induced by oxidation of P-870. The change of the carotenoid spectrum can therefore be correlated with the appearance of positive charge in the reaction center. In these studies we observed that at 35 K the absorption band of reaction center bacteriochlorophyll near 600 nm exhibits a shoulder at 605 nm. The resolution into two components is more pronounced in the light-dark difference spectrum. This observation is consistent with our earlier finding, that the "special pair" of bacteriochlorophyll molecules that acts as photochemical electron donor has a dimer-like absorption spectrum in the near infrared.
A structural role of the carotenoid in the light-harvesting II protein of Rhodobacter capsulatus
Biochemical Journal, 1993
The membrane-linked light-harvesting II protein (LHII) of Rhodobacter capsulatus was partly depleted of carotenoids by selective extraction with light petroleum. Carotenoid removal was accompanied by bleaching of the Qy(S1<--S0) absorption band of bacteriochlorophyll (Bchl) a near 800 nm, by a bathochromic shift and a broadening of the other Bchl Qy band at 850 nm, and by the formation of a weak Qy band of dissociated Bchl near 770 nm. The changes in the 800 and 850 nm bands seemed to reflect alterations in only those Bchl molecules that had lost their associated carotenoids, firstly, because the extent of the changes was closely correlated to the degree of carotenoid extraction, and, secondly, because the residual fraction of carotenoid-containing LHII, which could be almost quantitatively recovered from the membrane after detergent solubilization and ion-exchange chromatography, showed an unmodified LHII absorption spectrum. The Bchl responsible for the shifted 850 nm band rema...
The carotenoid shift in Rhodopseudomonas sphaeroides. Change induced under continuous illumination
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1977
The spectrum of the carotenoid shift generated under continuous illumination in the G1C mutant of Rhodopseudomonas sphaeroides, which has a single carotenoid, has been examined under a variety of conditions expected to alter the size of the membrane potential. If the difference spectrum observed was due to a species with the spectrum of the bulk pigment, it would correspond to a change of a variable proportion of the pigment to a form absorbing at a higher wavelength. The maximal change induced by light could be described as a shift of about 10 ~o of the pigment by 7 nm to the red, assuming that the shifted species was speetrally identical to the bulk carotenoid.
Dimeric carotenoid interaction in the light-harvesting antenna of purple phototrophic bacteria
The Biochemical journal, 1991
The carotenoid content of intracytoplasmic membrane vesicles isolated from purple phototrophic bacteria was reduced to a variable extent by mild extraction with light petroleum. Using preparations obtained from Rhodobacter capsulatus strains that contained the Light Harvesting System I (LHI) complex as the only major photosynthetic holochrome, it was shown that the visible circular dichroism of the carotenoids increased with the square of the membrane carotenoid content, as expected from being caused by dimeric exciton interaction. No chirality resulting from twists of the individual planar chromophore was detected. Therefore the contribution to carotenoid optical activity of non-degenerate interactions with bacteriochlorophyll or the apoprotein does not appear to be significant. The broadening of the absorption band of the bound pigment, caused by the splitting of the monomer transition, was demonstrated in membrane vesicles of both Rb, capsulatus and Rhodospirillum rubrum as a dec...
Changes in the native carotenoid of bacterial pigment-protein complexes
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1989
Changes in the carotenoid pool of the photosynthetic membrane of Rhodospirillum rubrum caused parallel changes in the carotenoids of light-harvesting and reaction-center complexes. Thus, whereas complexes purified from exponentially growing cultures contained spirilloxanthin and several of its colored metabolic precursors at comparable levels, only spirilioxanthin was detected in preparations derived from stationary-phase cultures, and in both cases the carotenoid composition of the isolated complexes was similar or identical to that of the intact membrane. The differences between the antenna pigments of stationary and exponential cultures were reflected in the circular dichroism spectrum and in the bacteriochlorophyli fluorescence excitation spectrum of the intact membrane, since both optical activity and singletsinglet energy transfer to bacteriochlorophyll are specific for complex-bound carotenoids. The changes in carotenoid composition that were induced by oxygen in cultures of Rhodobacter capsulatus were accompanied also by parallel changes in the pigments of both the core and the peripheral antenna complexes of this microorganism. In both species of purple bacteria, the variations of pigment pattern did not appear to influence to any significant extent the protective function of carotenoids, as assayed by following the photodestruction of antenna bacteriochlorophyll in aerobic suspensions of isolated membrane vesicles. The similar carotenoid composition of the intact membrane and the antenna may be simply explained by the limiting size of the pigment pool (all pigmented carotenoids that are present become complex-bound). However, to account for the carotenoid variability of the R. rubrum reaction center, which is less abundant in the membrane than some carotenoids, it seems necessary to assume that there are no significant differences among the binding affinities of the complex for the available pigments.
Photochemistry and Photobiology, 1993
,4-dihydrospheroidene a)1,d spheroidene, have been incorporated into the B850 light-harvesting complex of the carotenoidless mutant, photosynthetic bacterium, Rhodobacter sphaeroides R-26.1. The extent of 'If-electron conjugation in these molecules in,creases from 7 to 10 carbon-<:arbon double bonds. Carotenoid-to-bacteriochlorophyll singlet state energy transfer efliciencies were measured using steady-state fluorescence excitation spectroscopy to be 54 :t 2%, 66 :t 4%, 71 :t 611& and 56 :t 3% for the carotenoid series. These results are discussed with respect to the position of the energy levels and the magnitude of spectral overlap between the S, (2'AJ state emission from the isolated carotenoids and the bacteriochlorophyll absorption of the native complex. These studies provide a systematic approach to exploring the efl"ect of excited state energies, spectral overlap and excited state lifetimes on the efficiencies of carotenoid-tobacteriochlorophyll singlet energy transfer in photosynthetic systems.