Topography of reaction center subunits in the membrane of the photosynthetic bacterium, rhodopseudomonas sphaeroides.

Abstract

The localization of the reaction center polypeptides (L, M and H) in the membranes of both the wild-type, strain 2.4.1, and the carotenoidless mutant, R-26, of R. sphaeroides was determined by using affinity-purified antibodies specific for these proteins. Binding of the antibodies to reaction center subunits in spheroplasts was visualized in the EM by immunoferritin labeling. The H and M subunits were labeled at both the cytoplasmic and the periplasmic surfaces of the membrane, whereas the L subunit was labeled only at the periplasmic surface of the membrane. Thus, the reaction center is asymmetrically oriented in the membrane with at least 2 subunits (H and M) spanning the membrane.