Reaction: plastoquinol + 2 oxidized plastocyanin + 2 H+[side 1] = plastoquinone + 2 reduced plastocyanin + 4 H+[side 2]
Other name(s): plastoquinol/plastocyanin oxidoreductase; cytochrome f/b6 complex; cytochrome b6f complex
Systematic name: plastoquinol:oxidized-plastocyanin oxidoreductase
Comments: Contains two b-type cytochromes, two c-type cytochromes (cn and f), and a [2Fe-2S] Rieske cluster. The enzyme plays a key role in photosynthesis, transferring electrons from photosystem II (EC 220.127.116.11) to photosystem I (EC 18.104.22.168). Cytochrome c-552 can act as acceptor instead of plastocyanin, but more slowly. In chloroplasts, protons are translocated through the thylakoid membrane from the stroma to the lumen. The mechanism occurs through the Q cycle as in EC 22.214.171.124, quinolcytochrome-c reductase (complex III) and involves electron bifurcation.
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:
1. Hurt, E. and Hauska, G. A cytochrome f/b6 complex of five polypeptides with plastoquinol-plastocyanin-oxidoreductase activity from spinach chloroplasts. Eur. J. Biochem. 117 (1981) 591-595. [PMID: 6269845]
2. Cramer, W.A. and Zhang, H. Consequences of the structure of the cytochrome b6f complex for its charge transfer pathways. Biochim. Biophys. Acta 1757 (2006) 339-345. [PMID: 16787635]