Phylloquinone copurifies with the large subunit of photosystem I

Abstract

Photosystem I preparations from the cyanobacterium Anabaena variabilis and from spinach were analyzed for their quinone content. The dominant quinone was identified as phylloquinone. It was present at a ratio of roughly 2 per P700 (the primary electron donor of photosystem I) both in particles prepared with Triton X‐100 and on the large, P700‐carrying subunit derived from these particles by treatment with SDS. The results suggest a function of phylloquinone in the reaction center.