5'-Monohydroxyphylloquinone as a Component of Photosystem I

Abstract Thylakoids and photosystem I (PS I) preparations from Euglena gracilis and from the cyanobacterium Anacystis nidulans were analyzed for their prenylquinone content. Both organisms contained 5 '-monohydroxyphylloquinone as the dominant quinone of PS I, and not phylloquinone as other organisms. A stoichiometry of about two 5 '-monohydroxyphylloquinone per P700 (the primary electron donor of PS I) was determined for A nacystis. However, both the PS I preparation and the thylakoids from Euglena contained only one 5 '-monohydroxyphylloquinone per P700. Phylloquinone and an unidentified naphthoquinone were present in trace amounts.