Chlorophyll a′/P-700 and pheophytin a/P-680 stoichiometries in higher plants and cyanobacteria determined by HPLC analysis

The chlorophyll (CHl) a′ and pheophytin (Pheo) a contents in photosynthetic organs have been reinvestigated by means of silica HPLC. Previously reported data (Watanabe, T. et al. (1985) BBA 807, 110-117 and FEBS Lett. 191, 252-256) were found to contain errors from two sources: slight epimerization and pheophytinization of Chl a during pigment extraction and PS I particle preparation, and an accidental overlap of a Chl a alteration product (meso-chlorinated Chl a) with Chl a′ on the HPLC trace. The pigment molar ratios determined with the improved extraction/HPLC procedure were Chl a/Chl a′ ÷ 460 and Chl a/Pheo a ÷ 120 in more than 100 samples from 13 different higher plants, and Chl a/Chl a′ ÷ 125 and Chl a/Pheo a ÷ 100 in three cyanobacteria. These values, when combined with the PS I particle composition (Chl a′/P-700 = 1) and the widely accepted molar ratio Pheo a/P-680 of 2, yield P-680/P-700 = 1.9 ± 0.5 and 0.65 ± 0.20 as reaction center stoichiometries in higher plants and cyanobacteria, respectively. The present results correspond well with the recently published Chl a/reaction center stoichiometry data acquired by (photo-)redox titrations of key components.