A large photoreactive particle from Chromatium vinosum chromatophores

Large photoreactive particles from Chromatium vinosum are obtained pure and in high yield by using a mixture of detergents at high ionic strength to dissociate the chromatophore membrane. The particles contain all of the secondary electron acceptor of the chromatophores and about half of the cytochrome. Their content of ubiquinone is greatly enriched as compared with chromatophores. The individual particles have an estimated molecular weight of between 650 000 and 810 000.Gel electrophoresis of the preparation in sodium dodecylsulfate shows polypeptides with molecular weights of 50–45 000, 30 000, 27 000, 22 000 and 12 000. The 50–45 000 components are cytochromes. The 30 000, 27 000 and 22 000 components may be analogous to the triad of polypeptides present in Rhodopseudomonas spheroides reaction centers. The non-cytochrome components are partly soluble in chloroform/methanol.Aggregates of particles appear in these preparations. Electron microscopy of the aggregates demonstrates rectilinear lattices of isodiametric particles, 120 Å in diameter. These sheet-like structures are one unit thick and typically contain 9–16 members. They appear to arise by aggregation during isolation but are probably similar to native aggregates apparent within chromatophores after treatment with detergents at low salt concentration.