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Reversed‐phase HPLC determination of chlorophyll a ′ and phylloquinone in Photosystem I of oxygenic photosynthetic organisms

2003; Wiley; Volume: 270; Issue: 11 Linguagem: Inglês

10.1046/j.1432-1033.2003.03616.x

1432-1033

Akimasa Nakamura, Masahiko Akai, Emi Yoshida, Takashi Taki, Tadashi Watanabe,

Spectroscopy and Quantum Chemical Studies

Chlorophyll (Chl) a ′, the C13 2 ‐epimer of Chl a , is a constituent of the primary electron donor (P700) of Photosystem (PS) I of a thermophilic cyanobacterium Synechococcus ( Thermosynechococcus ) elongatus , as was recently demonstrated by X‐ray crystallography. To determine whether PS I of oxygenic photosynthetic organisms universally contains one molecule of Chl a ′, pigment compositions of thylakoid membranes and PS I complexes isolated from the cyanobacteria T. elongatus and Synechocystis sp. PCC 6803, the green alga Chlamydomonas reinhardtii , and the green plant spinach, were examined by simultaneous detection of phylloquinone (the secondary electron acceptor of PS I) and Chl a ′ by reversed‐phase HPLC. The results were compared with the Chl a /P700 ratio determined spectrophotometrically. The Chl a ′/PS I ratios of thylakoid membranes and PS I were about 1 for all the organisms examined, and one Chl a ′ molecule was found in PS I even after most of the peripheral subunits were removed. Chl a ′ showed a characteristic extraction behaviour significantly different from the bulk Chl a in acetone/methanol extraction upon varying the mixing ratio. These findings confirm that a single Chl a ′ molecule in P700 is the universal feature of PS I of the Chl a ‐based oxygenic photosynthetic organisms.