The pigment complement of the photosynthetic reaction center isolated from Rhodospirillum rubrum.

Isolated photosynthetic reaction center from the bacterium Rhodospirillum rubrum was extracted with acetone-methanol. Its main pigments were identified as bacteriochlorophyll, bacteriopheophytin, and spirilloxanthin. The extinction coefficients of these pigments in acetone-methanol were determined. Quantitative spectroscopic analysis of the dry acetone-methanol extracts indicated a bacteriochlorophyll to bacteriopheophytin mole ratio of 2 and led to an extinction coefficient at 868 nm of 71.3, 142.6, or 214 rnM-l cm-l, depending on whether the photosynthetic center was assumed to contain 2, 4, or 6 bacteriochlorophyll molecules. The extinction coefficient of PST,, was determined by mixing photo-oxidized photosynthetic center with ferrocytochrome c in a stopped flow spectrophotometer. Complete reaction was observed when the reactants were mixed in equimolar ratio calculated on the basis of an extinction coefficient of 143 rnr@ cm-l at 868 nm. This photosynthetic center is proposed to contain 4 moles of bacteriochlorophyll, 2 moles of bacteriopheophytin, and 1 mole of spirilloxanthin per equivalent of Pm.