Is There a Proteic Substructure Common to all Photosynthetic Reaction Centers ?

Abstract

In oxygen-evolving organisms, two sequential light-driven reactions occur in two distinct membrane-bound chlorophyll-protein complexes, namely PS2 and PS1. In purple bacteria (Rhodospirillales), use of the energy of light requires only one photoreaction, which occurs in the membrane-bound bacterial reaction center (RC). The bacterial RC shares a number of common functional properties with PS2 (1). Moreover, it has been shown that a highly significant degree of sequence homology exists between the two membrane-embedded subunits of the bacterial RCs (L and M) and the two subunits of the PS2 which are the location of the primary electron transfers, namely D1 and D2 (2). Unlike PS2, PS1 has not benefited from the analogy to the bacterial reaction center and many questions concerning its structure remain unresolved. Nevertheless, the sequence of the polypeptides, psa A and psa B, thought to carry the first electron carriers in PS1 was obtained for maize in 1985 (3).