Plastoquinone as a mobile redox carrier in the photosynthetic membrane

AbstractThe role of plastoquinone as a mobile redox carrier linking photosystem II and the cytochrome b6−f complex is considered. It is proposed that plastoquinone is located primarily within the fluid bilayer-midplane region of the thylakoid membrane and thus can move laterally at very fast rates corresponding to a microscopic diffusion coefficient of 10−6 cm2·s−1. Because of the presence of integral proteins the diffusion path will be tortuous and extended, giving rise to a sub-macroscopic diffusion coefficient which is lower than the above value. Even so it is concluded that within the half-time for electron donation to the cytochrome b6−f complex there is adequate time for plastoquinone to diffuse over a distance equivalent to the radius of a granum membrane