Photosynthetic electron transfer in Heliobacterium chlorum studied by EPR spectroscopy

Fischer, Monika

doi:10.1016/0005-2728(90)90081-e

Cited by 25 publications

(24 citation statements)

References 31 publications

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“…A similar result occurs in PSI where recovery from double reduction of A 1 requires a prolonged dialysis step to return to the initial state (Bottin and Setif 1991). The above results along with the EPR results (Fischer 1990) are consistent with the assignment of a quinone molecule as the acceptor, A1, in heliobacterial RCs. It will be interesting to find out the effect on electron transfer kinetics after addition of various quinones as well as results of extractionreconstitution studies on isolated RCs.…”

Section: Discussionsupporting

confidence: 77%

“…From the arguments presented above as well as the relatively long life of the P800 ÷ even in isolated RCs, we think that an Fe-S center similar to Fe-S x is functioning in heliobacterial RCs. Also similar to what is found in PSI, light-induced EPR signals have been observed in membranes from H. chlorum (Brok et al 1986, Fischer 1990) that have the characteristics of a quinone anion radical, although in PSI the interpretation of these EPR signals is controversial (Ziegler et al 1987, Barry et al 1988. A third line of evidence for a quinone-like A 1 acceptor in Heliobacterial RCs is based on our finding of a two-electron fit to the redox titration of millisecond recovery of PS00 photobleaching (Fig.…”

Section: Discussionsupporting

confidence: 51%

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Protein sequences and redox titrations indicate that the electron acceptors in reaction centers from heliobacteria are similar to Photosystem I

1992

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Photosynthetic reaction centers isolated from Heliobacillus mobilis exhibit a single major protein on SDS-PAGE of 47 000 Mr. Attempts to sequence the reaction center polypeptide indicated that the N-terminus is blocked. After enzymatic and chemical cleavage, four peptide fragments were sequenced from the Heliobacillus mobilis apoprotein. Only one of these sequences showed significant specific similarity to any of the protein and deduced protein sequences in the GenBank data base. This fragment is identical with 56% of the residues, including both cysteines, found in highly conserved region that is proposed to bind iron-sulfur center Fx in the Photosystem I reaction center peptide that is the psaB gene product. The similarity to the psaA gene product in this region is 48%. Redox titrations of laser-flash-induced photobleaching with millisecond decay kinetics on isolated reaction centers from Heliobacterium gestii indicate a midpoint potential of -414 mV with n = 2 titration behavior. In membranes, the behavior is intermediate between n = 1 and n = 2, and the apparent midpoint potential is -444 mV. This is compared to the behavior in Photosystem I, where the intermediate electron acceptor A1, thought to be a phylloquinone molecule, has been proposed to undergo a double reduction at low redox potentials in the presence of viologen redox mediators. These results strongly suggest that the acceptor side electron transfer system in reaction centers from heliobacteria is indeed analogous to that found in Photosystem I. The sequence similarities indicate that the divergence of the heliobacteria from the Photosystem I line occurred before the gene duplication and subsequent divergence that lead to the heterodimeric protein core of the Photosystem I reaction center.

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Section: Discussionsupporting

confidence: 77%

Section: Discussionsupporting

confidence: 51%

Protein sequences and redox titrations indicate that the electron acceptors in reaction centers from heliobacteria are similar to Photosystem I

1992

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“…This assessment is supported by the fact that the reported g-values of F X -are similar to those of F A -/F B -, and by the fact that the signal is not present when the F A and F B clusters are missing. Earlier, a light-induced EPR signal had been published on the Fe/S clusters in H. chlorum using a similar technique (Fischer 1990), and was noted as a possible heating artifact in a later study ).…”

Section: Intermediate Electron Acceptor F Xmentioning

confidence: 92%

Heliobacterial photosynthesis

Heinnickel

Golbeck

2007

Photosynth Res

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Heliobacteria contain Type I reaction centers (RCs) and a homodimeric core, but unlike green sulfur bacteria, they do not contain an extended antenna system. Given their simplicity, the heliobacterial RC (HbRC) should be ideal for the study of a prototypical homodimeric RC. However, there exist enormous gaps in our knowledge, particularly with regard to the nature of the secondary and tertiary electron acceptors. To paraphrase S. Neerken and J. Amesz (2001 Biochim Biophys Acta 1507:278-290): with the sole exception of primary charge separation, little progress has been made in recent years on the HbRC, either with respect to the polypeptide composition, or the nature of the electron acceptor chain, or the kinetics of forward and backward electron transfer. This situation, however, has changed. First, the low molecular mass polypeptide that contains the terminal FA and FB iron-sulfur clusters has been identified. The change in the lifetime of the flash-induced kinetics from 75 ms to 15 ms on its removal shows that the former arises from the P798+ [FA/FB]- recombination, and the latter from P798+ FX- recombination. Second, FX has been identified in HbRC cores by EPR and Mössbauer spectroscopy, and shown to be a [4Fe-4S]1+,2+ cluster with a ground spin state of S=3/2. Since all of the iron in HbRC cores is in the FX cluster, a ratio of approximately 22 Bchl g/P798 could be calculated from chemical assays of non-heme iron and Bchl g. Third, the N-terminal amino acid sequence of the FA/FB-containing polypeptide led to the identification and cloning of its gene. The expressed protein can be rebound to isolated HbRC cores, thereby regaining both the 75 ms kinetic phase resulting from P798+ [FA/FB]- recombination and the light-induced EPR resonances of FA- and FB-. The gene was named 'pshB' and the protein 'PshB' in keeping with the accepted nomenclature for Type I RCs. This article reviews the current state of knowledge on the structure and function of the HbRC.

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“…6 from Sattley et al 2008). Although much work over the past 25 years has contributed to our current understanding of heliobacterial electron transfer (Nuijs et al 1985;Smit et al 1987;Vos et al 1989;Fischer 1990;Trost et al 1992;Kleinherenbrink et al 1994;Lin et al 1995;Nitschke et al 1995;Kramer et al 1997;Oh-oka et al 2002;Heinnickel et al 2006, some important questions remain. Until recently, the nature and identity of the complex that transfers electrons from NADH to the menaquinone pool was unknown.…”

Section: Photosynthesis and Electron Transfermentioning

confidence: 97%

Insights into heliobacterial photosynthesis and physiology from the genome of Heliobacterium modesticaldum

Sattley

Blankenship

2010

Photosynth Res

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The complete annotated genome sequence of Heliobacterium modesticaldum strain Ice1 provides our first glimpse into the genetic potential of the Heliobacteriaceae, a unique family of anoxygenic phototrophic bacteria. H. modesticaldum str. Ice1 is the first completely sequenced phototrophic representative of the Firmicutes, and heliobacteria are the only phototrophic members of this large bacterial phylum. The H. modesticaldum genome consists of a single 3.1-Mb circular chromosome with no plasmids. Of special interest are genomic features that lend insight to the physiology and ecology of heliobacteria, including the genetic inventory of the photosynthesis gene cluster. Genes involved in transport, photosynthesis, and central intermediary metabolism are described and catalogued. The obligately heterotrophic metabolism of heliobacteria is a key feature of the physiology and evolution of these phototrophs. The conspicuous absence of recognizable genes encoding the enzyme ATP-citrate lyase prevents autotrophic growth via the reverse citric acid cycle in heliobacteria, thus being a distinguishing differential characteristic between heliobacteria and green sulfur bacteria. The identities of electron carriers that enable energy conservation by cyclic light-driven electron transfer remain in question.

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Photosynthetic electron transfer in Heliobacterium chlorum studied by EPR spectroscopy

Cited by 25 publications

References 31 publications

Protein sequences and redox titrations indicate that the electron acceptors in reaction centers from heliobacteria are similar to Photosystem I

Protein sequences and redox titrations indicate that the electron acceptors in reaction centers from heliobacteria are similar to Photosystem I

Heliobacterial photosynthesis

Insights into heliobacterial photosynthesis and physiology from the genome of Heliobacterium modesticaldum

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