Redox activities of mono- and binuclear forms of low-molecular and protein-bound dinitrosyl iron complexes with thiol-containing ligands

Abstract EPR, optical, electrochemical and stopped-flow methods were used to demonstrate that Fe(NO) 2 fragments in paramagnetic mononuclear and diamagnetic binuclear forms of dinitrosyl iron complexes with glutathione are reversibly reduced by a two-electron mechanism to be further transformed from the initial state with d 7 configuration into states with the d 8 and d 9 electronic configurations of the iron atom. Under these conditions, both forms of DNIC display identical optical and EPR characteristics in state d 9 suggesting that reduction of the binuclear form of DNIC initiates their reversible decomposition into two mononuclear dinitrosyl iron fragments, one of which is EPR-silent (d 8 ) and the other one is EPR-active (d 9 ). Both forms of DNIC produce EPR signals with the following values of the g -factor: g ⊥  = 2.01, g ||  = 1.97, g aver.  = 2.0. M-DNIC with glutathione manifest an ability to pass into state d 9 , however, only in solutions with a low content of free glutathione. Similar transitions were established for protein-bound М- and B-DNIC with thiol-containing ligands.