Antenna holochrome B880 of Rhodospirillum rubrum S1. Pigment, phospholipid, and polypeptide composition

Picorel, Rafael; Bélanger, Gilles; Gingras, G

doi:10.1021/bi00279a028

Cited by 107 publications

(102 citation statements)

References 18 publications

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“…The absorption spectra of such crystals were identical to those of purified native complexes (Cogdell et al, 1982;Picorel et al, 1983) showing a near-IR absorption maximum at 880 nm (data not shown). We have also measured the picosecond kinetics of energy transfer amongst BChl a pigments in such 2-D crystals.…”

Section: Resultsmentioning

confidence: 57%

“…In this paper we describe the projection structure of the LHC I from Rhodospirillum rubrum. R.rubrum contains only a single LHC with a-and f-polypeptides containing 52 and 54 amino acid residues, respectively (Cuendet and Zuber, 1977;Picorel et al, 1983;Brunisholz et al, 1984). Both polypeptides are predicted to possess a single transmembrane a-helix which for the a-subunit has been shown, by photolabelling studies, to be positioned between residues 11 and 29 (Meister et al, 1985).…”

Section: Introductionmentioning

confidence: 99%

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8.5 Å Projection Map of the Light-Harvesting Complex I from Rhodospirillum Rubrum Reveals a Ring Composed of 16 Subunits

Karrasch¹,

Bullough²,

Ghosh³

1995

Photosynthesis: From Light to Biosphere

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Section: Resultsmentioning

confidence: 57%

Section: Introductionmentioning

confidence: 99%

8.5 Å Projection Map of the Light-Harvesting Complex I from Rhodospirillum Rubrum Reveals a Ring Composed of 16 Subunits

Karrasch¹,

Bullough²,

Ghosh³

1995

Photosynthesis: From Light to Biosphere

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“…If the minimal subunit of the B880 holochrome is taken to contain two molecules of bacteriochlorophyll associated with a mass of 23 kDa [16], this would indicate an hexameric quaternary structure for this holochrome in vitro as well as in vivo. Large aggregates of the bacterial holochromes have also been implied by other methods [20, 22, 43, 441. Despite this qualitative agreement, the interpretation that we propose should be accepted with due caution since it is based on a model [41] that seems to apply to bacteriochlorophyllcontaining systems but that may not be universal, as illustrated by the case of the chlorophyll-a-containing primary donor of plant photosystem I [45, 461.…”

Section: Discussionmentioning

confidence: 99%

“…rubrum, two molecules of bacteriochlorophyll and one molecule of spirilloxanthin are associated with these polypeptides of Mr 5000 -6000. Furthermore, the pigment and protein composition of this preparation suggests that its minimal M, is approximately 23000 with an a2/j2 structure [16].…”

mentioning

confidence: 87%

Oxido‐reduction of B800–850 and B880 holochromes isolated from three species of photosynthetic bacteria as studied by electron‐paramagnetic resonance and optical spectroscopy

Picorel

Lefebvre

Gingras

1984

European Journal of Biochemistry

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Certain redox properties of bacteriochlorophyll a were used to probe the structure of several light-harvesting pigment-protein complexes or holochromes. To attribute redox properties unequivocally to a given holochrome, we worked with purified holochromes. We developed purification procedures for the B880 holochromes from Rhodospirillum rubrum, Rhodopseudomonas sphaeroides and Ectotliiorhodospira sp. and for the B800 -850 holochromes from the latter two species. In all these holochromes, bacteriochlorophyll a could be oxidized by ferricyanide as witnessed by the bleaching of their near-infrared absorption bands. However, only in B880 holochromes was this oxidation reversible. Another important difference between the B800-850 and the B880 holochromes is that oxidation of the latter gives rise to a g = 2.0025 electron paramagnetic resonance (EPR) signal with linewidth varying, according to species, from 0.37mT to 0.48mT. Both the reversible EPR signal and absorption changes titrate with a midpoint redox potential (pH 8.0) of approximately 570 mV. Linewidth narrowing can be interpreted by delocalization of the free electron spin over approximately 12 bacteriochlorophyll molecules. While the B880 holochromes from the three species considered had indistinguishable redox properties, the B800 -850 holochromes differed from one another by their circular dichroic spectra and by the relative ease of oxidation of their 800-nm and 850-nm bands. This indicates that, contrary to the B880 holochromes, the B800-850 holochromes may not form a homogeneous class.

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“…Membrane fragments from R. rubrum S1 were prepared as described in (9). Isolated LH1 complexes devoid of RCs were obtained as described in (10). A HPLC assay indicated that exclusively BChl a and Spx were present in this preparation.…”

Section: Methodsmentioning

confidence: 99%

An unusual pathway of excitation energy deactivation in carotenoids: Singlet-to-triplet conversion on an ultrafast timescale in a photosynthetic antenna

Gradinaru

Kennis

Papagiannakis

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

342

611

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Carotenoids are important biomolecules that are ubiquitous in nature and find widespread application in medicine. In photosynthesis, they have a large role in light harvesting (LH) and photoprotection. They exert their LH function by donating their excited singlet state to nearby (bacterio)chlorophyll molecules. In photosynthetic bacteria, the efficiency of this energy transfer process can be as low as 30%. Here, we present evidence that an unusual pathway of excited state relaxation in carotenoids underlies this poor LH function, by which carotenoid triplet states are generated directly from carotenoid singlet states. This pathway, operative on a femtosecond and picosecond timescale, involves an intermediate state, which we identify as a new, hitherto uncharacterized carotenoid singlet excited state. In LH complex-bound carotenoids, this state is the precursor on the reaction pathway to the triplet state, whereas in extracted carotenoids in solution, this state returns to the singlet ground state without forming any triplets. We discuss the possible identity of this excited state and argue that fission of the singlet state into a pair of triplet states on individual carotenoid molecules constitutes the mechanism by which the triplets are generated. This is, to our knowledge, the first ever direct observation of a singlet-to-triplet conversion process on an ultrafast timescale in a photosynthetic antenna. C arotenoids (Cars) serve a variety of functions in biological systems. In photosynthesis, they act as light-harvesting (LH) pigments by absorbing sunlight in the blue and green parts of the solar spectrum and transferring the excited state energy to nearby (bacterio)chlorophylls (BChl) (1, 2). The BChl molecules subsequently transfer this energy to a photochemical energyconverting protein known as the reaction center (RC), where the excited state energy is fixed by means of a series of electron transfer reactions (3). During these energy-and electrontransfer processes, which may take up to hundreds of picoseconds, the singlet excited and charge-separated states of BChl are subject to intersystem crossing to the triplet state, which occurs on a timescale of several nanoseconds. Although produced with a small probability, these BChl triplet states are potentially harmful to the organism because they can promote molecular oxygen to its singlet excited state, which is a highly reactive and damaging species. Cars can efficiently accept and safely dissipate BChl triplet and singlet oxygen states, and this photoprotective quality is utilized by essentially all photosynthetic organisms (1, 2).The first singlet excited state of Cars, S 1 , carries gerade symmetry (with respect to inversion) as does the ground state, S 0 , and is therefore dipole-forbidden. The second excited singlet state, S 2 , carries ungerade symmetry and is dipole-allowed (1). The specific strong Car absorption in the blue and green regions of the visible part of the electromagnetic spectrum is caused by the transition to this second excited state,...

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Antenna holochrome B880 of Rhodospirillum rubrum S1. Pigment, phospholipid, and polypeptide composition

Cited by 107 publications

References 18 publications

8.5 Å Projection Map of the Light-Harvesting Complex I from Rhodospirillum Rubrum Reveals a Ring Composed of 16 Subunits

8.5 Å Projection Map of the Light-Harvesting Complex I from Rhodospirillum Rubrum Reveals a Ring Composed of 16 Subunits

Oxido‐reduction of B800–850 and B880 holochromes isolated from three species of photosynthetic bacteria as studied by electron‐paramagnetic resonance and optical spectroscopy

An unusual pathway of excitation energy deactivation in carotenoids: Singlet-to-triplet conversion on an ultrafast timescale in a photosynthetic antenna

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