Local Environments of Pigments in Reaction Centers of Photosynthetic Bacteria from Resonance Raman Data

Abstract

Reaction centers from purple photosynthetic bacteria (Rhodospirillales) appear to generally contain two identical sets of pigments. One of these sets is predominantly (but most probably not exclusively, ref. 1) involved in the primary electron-transfers. Recent X-ray crystallographic data on reaction centers (RCs) from Rhodopseudomonas viridis show that these two sets of pigments are symmetrically arranged within the proteic core along a C₂ axis (2). The relative orientations and distances of molecules are very much the same in the two sets. Spectroscopic data indicate an identical situation in RCs from Rps. sphaeroides (3). Hence the very different electron-transfer properties of the two sets must largely result from differences in local environments, which may, in particular, result in different redox potentials of molecules in the two sets (4). These local environments still cannot be determined in a detailed fashion from X-ray data.