... that of a flavin-based radical pair in photolyase (Fig. 5C) [2]. Analysis of the spectralshapes of TREPR signals yields information on the chemical nature of the individual radicals of the radi-cal ... transitions belonging to one of the two b-protons, H(1 ¢), attached to C(1¢) in the ribitylside chain of the isoalloxazine ring [39]. (d) Signalsarising from hyperfine coupling of the H(6) protonoccur ... [28,35,36,41–45]. In pulsed ENDORexperiments, the ENDOR signal is obtained by record-ing the echo intensity as a function of the frequency of a radiofrequency pulse. Changes in the echo intensityoccur...