title: On the spatial organization of hemes and chlorophyll in cytochrome b(6)f. A linear and circular dichroism study.
abstract: The organization of chromophores in the cytochrome b(6) f from Chlamydomonas reinhardtii has been studied spectroscopically. Linear dichroism (LD) measurements, performed on the complex co-reconstituted into vesicles with photosynthetic reaction centers as an internal standard, allow the determination of the orientations of the chromophore with respect to the membrane plane. The orientations of the b(H)- and b(L)-hemes are comparable to those determined crystallographically on the cytochrome bc(1). The excitonic CD signal, resulting from the interaction between b-hemes, is similar to that reported for the cytochrome bc(1). LD and CD data are consistent with the differences between the b(6) f and bc(1) leaving the orientation of the b-hemes unaffected. By contrast, the LD data yield a different orientation for the heme f as compared either to the heme c(1) in the crystallographic structures or to the heme f as studied by electron paramagnetic resonance. This difference could either result from incorrect assumptions regarding the orientations of the electronic transitions of the f-heme or may point to the possibility of a redox-dependent movement of cytochrome f. The chlorophyll a was observed in a well defined orientation, further corroborating a specific binding site for it in the b(6) f complex.
authors.affiliation: Laboratoire de Bioénergétique et Ingénierie des Protéines, CNRS 31, Chemin Joseph Aiguier, F-13402 Marseille Cedex 20, France.
authors.forename: B
authors.initials: B
authors.lastname: Schoepp
authors.forename: E
authors.initials: E
authors.lastname: Chabaud
authors.forename: C
authors.initials: C
authors.lastname: Breyton
authors.forename: A
authors.initials: A
authors.lastname: Verméglio
authors.forename: J L
authors.initials: JL
authors.lastname: Popot
mesh_terms: D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000737:chemistry; D002734:Chlorophyll / Q000737:chemistry*; D002942:Circular Dichroism; D003573:Cytochrome b Group / Q000737:chemistry*; D045346:Cytochrome b6f Complex; D003580:Cytochromes / Q000737:chemistry; D045348:Cytochromes f; D014450:Electron Transport Complex III / Q000737:chemistry; D006418:Heme / Q000737:chemistry*; D008081:Liposomes / Q000378:metabolism; D010084:Oxidation-Reduction; D011485:Protein Binding; D011487:Protein Conformation; D013053:Spectrophotometry
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D008081:Liposomes; D002734:Chlorophyll; D006418:Heme; D045346:Cytochrome b6f Complex; D045348:Cytochromes f; D014450:Electron Transport Complex III