Pigment stoichiometry of a newly isolated D1—D2—Cyt b559 complex from the higher plant Beta vulgaris L.

Abstract

Two D1-D2-Cyt b559 complexes with different pigment stoichiometry were isolated from the higher plant B. vulgaris. The procedures for isolating both complexes only differed in the washing time of the DEAE column with 50 mM Tris-HCl, pH 7.2, 0.05% Triton X-100 and 30 mM NaCl. When the column was washed until the eluate had an absorbance of 0.01 at 670 nm, the isolated D1—D2—Cyt b559 complex presented a pigment stoichiometry of 6 chlorophyll a, 2 β-carotene, and 1 cytochrome b559 per 2 pheophytin a. In contrast, when the column was exhaustively washed until the eluate reached an absorbance of 0.005 at 670 nm, the complex had a stoichiometry of 4 chlorophyll a, 1 β-carotene, and 1 cytochrome b559 per 2 pheophytin a. We think that the former stoichiometry corresponds to that of the native D1—D2—Cyt b559 complex. Moreover, both preparations showed 2 mol of pheophytin a per 1 mol of reaction center protein.