Analytical Sciences

Reversed-phase HPLC Determination ofChlorophyll a' and Naphthoquinones in Photosystem I of Red Algae:Existence of Two Menaquinone-4 Molecules in Photosystem I of Cyanidiumcaldarium

Emi YOSHIDA, Akimasa NAKAMURA, andTadashi WATANABE 

Institute of Industrial Science, TheUniversity of Tokyo, Komaba, Meguro, Tokyo 153-8505, Japan

Chlorophyll (Chl) a', theC13²-epimer of Chl a, is one of the two Chl moleculesconstituting the primary electron donor (P700) of photosystem (PS) I of athermophilic cyanobacterium Synechococcus elongatus. To examinewhether PS I of other oxygenic photosynthetic organisms in general containone Chl a' molecule in P700, the pigment composition of thylakoidmembranes and PS I preparations isolated from red algae Porphyridiumpurpureum and Cyanidium caldarium was examined by reversed-phaseHPLC with particular attention to Chl a' and phylloquinone (PhQ),the secondary electron acceptor of PS I. The two red algae contained oneChl a' molecule at the core part of PS I. In PS I of C.caldarium, two menaquinone-4 (MQ-4) molecules were detected in placeof PhQ used by higher plants and cyanobacteria. The 1:2:1 stoichiometryamong Chl a', PhQ (MQ-4) and P700 in PS I of the red algae indicatesthat one Chl a' molecule universally exists in PS I of oxygenicphotosynthetic organisms, and two MQ-4 molecules are associated with PS Iof C. caldarium.

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