Redox properties electron paramagnetic resonance

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The physical biochemistry of these two classes of 4Fe-4S proteins has been extensively studied and reviewed, especially with regard to redox and electron transfer chemistry (2-22), whereas the magnetic properties of the cluster have been probed by electron paramagnetic resonance (EPR) (23-34), nuclear magnetic resonance (NMR) (24, 25, 35-54), and susceptibility measurements (56-61). Mossbauer spec-... 

Photosystem II (PSII) contains a remarkably stable tyrosine radical D", located at tyr-160 in the D2 polypeptide, which exhibits a well-known electron paramagnetic resonance (EPR) spectrum, EPR Signal Ilg (1). The function of D" " in the mechanism of photosynthetic H2O oxidation remains unclear despite evidence that it can oxidize the Mn complex, the H20-oxidation catalyst in PSII, from the Sq state to the normally daik-stable Si state (2). Several studies indicate that die oxidation state of the Mn complex influences the electron spin-lattice relaxation rate of D" (3-5), perhaps via a weak dipolar coupling, as suggested by Evelo et al. (5). Hence, the relaxation properties of D may provide a probe for the topology of redox-active sites in the 02-evolving center (OEC) and of the magnetic properties of the Mn complex. 

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