Cytochrome b6-f complex iron-sulfur subunit <p>The cytochrome b6-f complex mediates electron transfer between photosystem II (PSII) and photosystem I (PSI), cyclic electron flow around PSI, and state transitions. The cytochrome b6-f complex has 4 large subunits, these are: cytochrome b6, subunit IV (17 kDa polypeptide, PetD), cytochrome f and the Rieske protein, while the 4 small subunits are: PetG, PetL, PetM and PetN. The complex functions as a dimer. </p><p>Proteins in this entry represent enzymatically active iron-sulphur subunit of the cytochrome b6-f complex:- Plastohydroquinone:plastocyanin oxidoreductase iron-sulphur protein which catalyses the reaction: <reaction>Plastoquinol-1 + 2 oxidized plastocyanin = plastoquinone + 2 reduced plastocyanin. </reaction>These proteins are located the cellular thylakoid membrane. The transmembrane helix obliquely spans the membrane in one monomer, and its extrinsic C-terminal domain is part of the other monomer. The Rieske iron-sulphur protein is a high potential 2Fe-2S protein which contains 1 Rieske domain.</p>