| Abstract
| - The flavin cofactor of Escherichia coli DNA photolyase in its neutral radical form, FADH•, was investigatedby high-frequency/high-field continuous-wave electron paramagnetic resonance at 360 GHz. The data presentedare the first flavin radical spectra where the full rhombic symmetry of the g-tensor is resolved. A fit of thespectrum yields accurate principal values of g, which show only a small anisotropy: gX = 2.004 31(5), gY =2.003 60(5) and gZ = 2.002 17(7). The hyperfine splitting observed in the gY region could be assigned to ahyperfine tensor component of the H(5) proton in the 7,8-dimethyl isoalloxazine moiety of FADH•. From acomparison of this effective hyperfine coupling with the principal value obtained from pulsed (Davies)electron−nuclear double resonance, the orientation of the g-tensor principal axes with respect to the H(5)hyperfine principal axes could be derived. Remaining ambiguities in the sign of the angle between the principalaxes of g and the molecular axes are discussed by taking into account results from g-tensor calculations usingdensity functional theory and semiempirical AM1 based methods.
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