The S0 State EPR Signal from the Mn Cluster in Photosystem II Arises from an Isolated S = 1/2 Ground State
During oxygen evolution, the Mn cluster in Photosystem II cycles through five oxidation states, S0-S4. S0 and S2 are paramagnetic, and can be monitored by electron paramagnetic resonance (EPR). Recently a new EPR signal from the S0 state was discovered [Åhrling et al. (1997) Biochemistry 36, 13148-13152, Messinger et al. (1997) J. Am. Chem. Soc. 119, 11349-11350]. Here, we present a well-resolved