DETERMINATION OF THE G TENSOR OF THE PRIMARY DONOR CATION RADICAL IN SINGLE-CRYSTALS OF RHODOBACTER-SPHAEROIDES R-26 REACTION CENTERS BY 3-MM HIGH-FIELD EPR

Three millimeter (W band, 95 GHz) EPR measurements were performed on single crystals of Rb. sphaeroides R-26 reaction centers at room temperature to determine the g tensor of the primary donor cation radical Ps6s.+. Due to the applied high magnetic field (3.4 T), the magnetically inequivalent sites in the unit cell of the crystals could be resolved. Some of the results are corroborated by additional measurements on P865.+ in perdeuterated reaction centers from Rb. sphaeroides wild type 2.4. 1, which could be crystallized for the first time. From this preparation the 3-mm EPR spectrum of P865.+ in frozen reaction center solution could be resolved into its three principal g tensor components. The principal directions of the g tensor in the single crystal reveal a breaking of the local C2 symmetry in the electronic structure of P865.+ consistent with earlier ENDOR results for the hyperfine structure.