<Li> Photo - reduction of pheophytin has been observed in various mixtures containing PSII reaction centers . </Li> <Li> The quantity of pheophytin is in direct proportion to the number of PSII reaction centers . </Li> <Li> Photo - reduction of pheophytin occurs at temperatures as low as 100K, and is observed after the reduction of plastoquinone . </Li> <P> These observations are all characteristic of photo - conversions of reaction center components . </P>

Phaeophytin is the electron acceptor molecule in photosystem 2