High Quality Content by WIKIPEDIA articles! The cytochrome b6f complex (plastoquinol—plastocyanin reductase; EC 1.10.99.1) is an enzyme found in the thylakoid membrane in chloroplasts of plants, cyanobacteria, and green algae, catalyzing the transfer of electrons from plastoquinol to plastocyanin. The reaction is analogous to the reaction catalyzed by cytochrome bc1 (Complex III) of the mitochondrial electron transport chain. For photosynthesis, the cytochrome b6f complex transfers electrons between the two reaction complexes from Photosystem II to Photosystem I, whereby introducing protons into the thylakoid space.