HIGH-FIELD EPR ON THE PRIMARY ELECTRON-DONOR CATION-RADICAL IN SINGLE-CRYSTALS OF HETERODIMER MUTANT REACTION CENTERS OF PHOTOSYNTHETIC BACTERIA - FIRST CHARACTERIZATION OF THE G-TENSOR

First high-field/high-frequency (95 GHz) EPR experiments on the cation radical of the primary electron donor (D) in single crystals of the H L (M202) heterodimer mutant of the photosynthetic bacterium Rhodobacte r sphaeroides are reported. The measurements have been performed in or der to determine the electronic G-tensor of D+ in the mutant and to co mpare it to the G-tensor of D+ in wild type (R-26). In the heterodimer mutant one of the two bacteriochlorophyll (BChl) molecules constituti ng D in R-26 is replaced by a bacteriopheophytin. In D+ of the mutant the unpaired electron is localized on the BChl, thus, its G-tensor sho uld reflect monomer properties, whereas in D+ of R-26 the unpaired ele ctron is delocalized over the two BChl molecules. The preliminary resu lts reported here show that directions of the principal axes of the G- tensor of D+ in HL (M202) are similar to those of R-26 investigated pr eviously. Possible origins of this result are discussed.