On the Spatial Organization of Hemes and Chlorophyll in Cytochrome b 6 f

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

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.