EPR STUDY OF TRAPPED TYROSINE Z(-DEPLETED PHOTOSYSTEM-II() IN CA)

The dependence of the light-induced transient EPR signal intensity of Y-Z(+) on the illumination temperature was measured in Ca-depleted PS II in the presence of DCMU, The maximum yield of Y-Z(+), about 70% of Y-D(+) EPR intensity, was obtained by illumination at 245 K, and trapp ed by immediate freezing in liquid nitrogen. Analysis of the relative intensities of Y-Z(+) and modified multiline EPR signals under various illumination periods and temperatures shows that Y-Z(+) has been trap ped in the S-1 state of the oxygen evolving center, and the trapped Y- Z(+) EPR converted to the multiline signal through the advancement fro m the S-1 to S-2 state in the dark at 273 K, Spin-lattice relaxation t imes of Y-D(+) and Y-Z(+) in the Ca-depleted and Mn-depleted PS II wer e measured by pulsed EPR. From the relaxation enhancements of these ra dicals due to the dipole interaction with the Mn cluster, the distance from Y-Z(+) to the Mn cluster was estimated to be 15-20 Angstrom. Usi ng the 2 + 1 ESE method, the distance between Y-Z(+) and Y-D(+) was de termined to be 29-30 Angstrom.