Evolutionary Relationships between Reaction Center Complexes with and without Cytochrome c Subunits in Purple Bacteria

Abstract

Two types of the photosynthetic reaction center (RC) complexes are known in purple bacteria, the distribution of which depends on bacterial species (1). In one type, the RC complexes have a cytochrome subunit with four c-type hemes. The other type of RC does not have the cytochrome subunit (Fig. 1). Three demensional structures of both types of RCs have been revealed in Rhodopseudomonas viridis (2) and Rhodobacter sphaeroides (3); the former has the bound cytochrome subunit. The major difference between the two types of RC is only in the presence or absence of the cytochrome subunit and the structure of the other three peptides with pigments and quinones is similar to each other. Evolutionary relationships between the two types of RC and the role of the bound cytochrome subunit are interesting subjects in the photosynthetic electron transfer system in purple bacteria.