Assignment of the g = 4.1 EPR signal to manganese in the S2 state of the photosynthetic oxygen-evolving complex: an X-ray absorption edge spectroscopy study

X-ray absorption spectroscopy at the Mn K-edge has been utilized to study the origin of the g = 4.1 EPR signal associated with the Mn-containing photosynthetic O2-evolving complex. Formation of the g = 4.1 signal by illumination of Photosystem II preparations at 140 K is associated with a shift of the Mn edge inflection point to higher energy. This shift is similar to that observed upon formation of the S2 multiline EPR signal by 190 K illumination. The g = 4.1 signal is assigned to the Mn complex in the S2 state.