The spin‐lattice relaxation of the tyrosine radical D. in Photosystem II particles was studied at 4.2 K in samples in which flash‐induced oscillations of the oxidation state of the Mn‐cluster of the oxygen evolving system were abolished by addition of ANT2P, leaving Fe2+/Fe3+ oscillations intact. Samples subjected to 0, 1 or 2 light‐flashes all showed the same relaxation kinetics. No period‐2 oscillation in the spin‐lattice relaxation corresponding to the Fe2+/Fe3‐‐oscillation was observed. Thus the T1‐oscillations of D. as a function of flash number in untreated samples are solely caused by the charge‐oscillations of the Mn‐cluster (1989, Biochim. Biophys. Acta 973, 428–442).
