Nature of photochemical reactions in chromatophores of Chromatium D. III. Heterogeneity of the photosynthetic units.

The effect of isooctane extraction on photooxidation of c-type cytochromes was investigated in Chromatium chromatophores. Photooxidation of cytochrome c-555 was not affected by isooctane-extraction was abolished by thorough extraction of ubiquinone-7, but the quantum yield of the cytochrome photooxidation remained unchanged until 90% of the total ubiquinone was extracted. The photooxidation of cytochrome c-552 was recovered by the addition of ubiquinone-7 but not by menaquinone. A dark incubation of sufficient length was needed for maximal quantum yield of cytochrome c-555 photooxidation in the presence of 30 mM ascorbate. It is proposed that there are two types of photosynthetic units (or associations of molecules involved in the primary redox reactions) in Chromatium chromatophores. The combinations of primary electron donor-reaction center chlorophyll-primary electron acceptor may be cytochrome c-552-P890=ubiquinone in one type and cytochrome c-555-P890-X in another.