Assembly of Intracytoplasmic Membranes in Rhodobacter Sphaeroides Mutants Lacking Light-Harvesting and Reaction Center Complexes

Abstract

The intracytoplasmic membrane (ICM) of photosynthetic bacteria contains a number of integral bacteriochlorophyll (BCh1)-protein complexes. In Rhodobacter sphaeroides, these consist of photochemical reaction centers together with the B800-850 and B875 light-harvesting proteins1 which function as peripheral and core antennae, respectively. The B875 and reaction center complexes form the fixed cores of photosynthetic units and are found in a constant molar ratio of ~25:1, respectively [2]. The B800-850 antenna comprises the variable portion of the photosynthetic unit and can reach levels more than three-fold greater than those of B875 under low illumination [2] or in the latter stages of induction of ICM formation at reduced oxygen tension [3]. The ICM is continuous with the cytoplasmic membrane [4, 5] and in vivo surface labeling has demonstrated that the interior of the ICM is accessible from the periplasmic space [6, 7].