Structural studies of the primary donor cation radical P-870+ in reaction centers of Rhodospirillum rubrum by electron-nuclear double resonance in solution
b'The light-induced cation radical of the primary\\nelectron donor, Ps70, in photosynthetic reaction centers\\nfrom Rhodospirillum rubrum G-9, has been investigated by\\nelectron-nuclear double resonance (ENDOR) in liquid aqueous\\nsolution. The measured hyperfine coupling constants are\\nassigned to specific molecular positions by partial deuteration.\\nComparison with the bacteriochlorophyll a cation radical\\nshows different reduction factors of the individual coupling\\nconstants deviating from the value 2.0 reported in earlier investigations\\nin frozen solutions. The average of the coupling\\nconstants is, however, reduced by a factor very close to 2.0.\\nEPR simulations using the ENDOR coupling constants support\\na dimer model for PsO with C2 symmetry, where the two macrocycles\\nare close enough to form a supermolecular orbital resulting\\nin a different distribution of the unpaired electron,\\ncompared with the monomeric bacteriochlorophyll a cation\\nradical. Molecular orbital calculations were used to obtain\\nstructural information about this dimer.'