On the Spatial Organization of Hemes and Chlorophyll in Cytochrome b6f

• Published in: The Journal of biological chemistry 2000-02, Vol.275 (8), p.5275-5283
• Main Authors: Schoepp, Barbara, Chabaud, Elodie, Breyton, Cécile, Verméglio, André, Popot, Jean-Luc
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.275.8.5275

The organization of chromophores in the cytochrome b6f fromChlamydomonas 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 bH- andbL-hemes are comparable to those determined crystallographically on the cytochrome bc1. The excitonic CD signal, resulting from the interaction betweenb-hemes, is similar to that reported for the cytochromebc1. LD and CD data are consistent with the differences between the b6f andbc1 leaving the orientation of theb-hemes unaffected. By contrast, the LD data yield a different orientation for the heme f as compared either to the heme c1 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 theb6f complex.