Quarternary Structure of the B875 Light-Harvesting Complex from Rhodospirillum Rubrum G9+

Abstract

The structure of the light-harvesting complexes in purple non-sulphur bacteria is a subject of intense research at present (see Zuber, 1985). A particularly well-characterized example is the B875 complex from Rhodospirillum rubrum. The single type of light-harvesting complex (B875) in this organism is formed from two non-identical polypeptides, α and β, respectively, and possess 2 mol bacteriochlorophyll (BCh1) and 1 mol spirilloxanthin/mol αβ dimer, respectively (Picorel et al. 1983). The sequences and topology of the complex have been determined (Brunishoiz et al. 1984, Meister et al. 1985, Brunisholz et al. 1986, Bachofen and Wiemken, 1986). However, the quarternary structure of the complex is a subject of some controversy (Miller et al. 1987, Ghosh et al. 1988, Hunter et al. 1988). Recently Loach and coworkers isolated a complex absorbing at 820nm (B820) which was suggested to be a subunit form of the B875 complex. However, the precise molecular weight of the complex and its in vivo significance remained unclear. In this paper we examine the molecular properties of the B820 complex in more detail and suggest a possible model for the role of the B820 complex in vivo.