Localization of photosynthetic reaction centers by antibody binding to chromatophore membranes from Rhodopseudomonas...

Rabbit antiserum against highly purified reaction center preparations was shown to react specifically with a single component of chromatophore membranes from Rhodopseudomonas spheroides strain R-26. The conjugate of purified gamma globulin and ferritin prepared with toluene diisocyanate was used to determine the localization of reaction centers in the chromatophore membranes. Virtually no antibody was bound by intact membranes. After removing the 9nm ATPase from these membranes by dilute EDTA treatment, a considerable amount of antibody was bound to the exposed outer membrane surface. The reaction center binding sites were estimated to be uniformly distributed with approx. 1 reaction center per 200 nm-2 of membrane surface. These results indicate that the reaction centers are located near the outer membrane surface but below the ATPase particles. Since the distribution of reaction centers and particles on rough faces seen by freeze-fracture particle may be a complex of a reaction center and other electron transfer components localized within the hydrophobic region of the membrane.