Characterization of a pseudo-B870 light-harvesting complex isolated from the mutant strain Ala +Pho − of Rhodobacter capsulatus which contains B800–850-type polypeptides

Abstract

A pseudo-B870 light-harvesting pigment complex was isolated from membranes of the phototroph negative mutant strain Ala+Pho− of Rhodobacter capsulatus by urea treatment of membranes, sucrose density gradient centrifugation and DEAE chromatography. The isolated pseudo-B870 complex has a major near-infrared absorption maximum at 869 nm as the B870 complex of the photosynthetically active parent strain Ala+Pho+. The isolated pseudo-B870 complex contains two bacteriochlorophyll-binding polypeptides which reacted with antibodies against the B800-850 complex of Rhodobacter capsulatus and had the same amino acid composition and the same C-terminal amino acid sequence as the α, β-polypeptides of the B800–850 complex. As shown by fluorescence emission spectroscopy excitation energy was transferred from pseudo-B870 to reaction center after fusion of pseudo-B870 membranes with proteoliposomes containing reaction centers. However, no efficient energetic coupling between pseudo-B870 and B800-850 light-harvesting complexes was observed.