The cytochrome b₆f complex (plastoquinol—plastocyanin reductase; ) is an enzyme found in the thylakoid membrane in chloroplasts of plants, cyanobacteria, and green algae, that catalyze 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. During photosynthesis, the cytochrome b₆f complex transfers electrons from Photosystem II to Photosystem I, whereby pumping protons into the thylakoid space and creating an electrochemical (energy) gradient where it is later used to create adenosine triphosphate (ATP).