EPR Characterization of Mononuclear Dinitrosyl Iron Complex with Persulfide as a New Representative of Dinitrosyl Iron Complexes in Biological Systems: an Overview

Some recent data on the presence of mononuclear dinitrosyl iron complexes (M-DNIC) with persulfide (R-S-S-) ligands with a characteristic electron paramagnetic resonance signal at g(perpendicular to) = 2.35 and g(parallel to|) = 2.02 (g(aver.) = 2.03) in biological systems (e.g., Escherichia coli cells and isolated iron-sulfur proteins) are reviewed. The generation of M-DNIC is controlled by inorganic sulfur (sulfide, S2-) whose binding to thiols gives persulfides. It is suggested that enhanced production of inorganic sulfur is a result of destruction of active centers of iron-sulfur proteins in the presence of NO or NO-containing compounds. Dinitrosyl iron complexes with thiol-containing ligands are the most active participants in this process. Inorganic sulfur may appear in biological systems during the synthesis or resynthesis of active centers of iron-sulfur proteins in response to activation of cysteine desulfurase, the key enzyme in sulfide synthesis from cysteine.