Plastoquinones QB and QA are two molecules that participate in the electron transfer system betweeen photosystem II (PSII) and photosystem I. The sequence of carriers is as follows: Pheophytin -> QA -> QB -> QH. Plastoquinone QB and QA are associated with PSII proteins. Electron transfer involving plastoquinones is shown here. Reduction of a plastoquinone creates a plastoquinol.

See also: Plastoquinones, Photosystem II, Photosystem I, Plastoquinone QH, Pheophytin, Plastoquinone QA