Cytochrome b6f is a dimeric protochlorophyll a binding complex in etioplasts

The cytochrome b(6)f complex is a dimeric protein complex that is of central importance for photosynthesis to carry out light driven electron and proton transfer in chloroplasts. One molecule of chlorophyll a was found to associate per cytochrome b(6)f monomer and the structural or functional importance of this is discussed. We show that etioplasts which are devoid of chlorophyll a already contain dimeric cytochrome b(6)f. However, the phytylated chlorophyll precursor protochlorophyll a, and not chlorophyll a, is associated with subunit b(6). The data imply that a phytylated tetrapyrrol is an essential structural requirement for assembly of cytochrome b(6)f.