Some Chemical and Physical Properties of a Bacterial Reaction Center Particle and Its Primary Photochemical Reactants*

A photochemically active protein‐chlorophyll complex (i.e. reaction center particle) has been isolated from Rhodopseudomonas spheroides R‐26. The isolation and purification procedure is outlined and some of the chemical and physical properties of the complex (e.g. amino acid composition, metal content, molecular weight) are presented. Two distinct ESR signals have been observed. They are attributed to the primary oxidation‐reduction couple. The experimental evidence which shows that the narrow ( g = 2.0026) signal is due to a bacterio‐chlorophyll free radical is reviewed. The possibility that the broad ESR signal is due to iron is discussed.