Fig. 2.

High-field 285-GHz EPR spectra of the generated in Mn-depleted PSII at low temperatures. (A) Baseline spectrum before illumination. (B) After illumination at 1.8 K. (C) Same sample warmed to 77 K for 10 min. (D) Solid line, same sample warmed to 200 K for 1 min; dashed line, similar sample (24) with the radical obtained at physiological temperatures. Spectra were obtained at 285 GHz at 4.2 K and were normalized averages of 8–16 scans obtained with a field modulation of 20 G. The dotted black lines from right to left are positioned at g-values of 2.00215, 2.00430, 2.00645, and 2.00756. (Inset) Comparison of the g_x region of radical obtained after 1.8-K illumination (10 G modulation, solid-line) and radical obtained at physiological temperatures (3 G modulation, dashed line, also shown in its entirety in D).