Conformational effect of thiol-compounds on the formation of a nitrosyl(protoporphyrinato)iron(II) complex adsorbed on a basic oxide of magnesium oxide powder with the nitrite ion

It has investigated using a Clark-type oxygen electrode and an ESR method that the conformation of thiol-compounds such as cysteine (Cys) and glutathione (GSH) effects on the formation of a nitrosyl(protoporphyrinato)iron(II) complex by the reaction between hydroxo(protoporphyrinato)iron(III) complex adsorbed on magnesium oxide (Heme/MgO) powder and the nitrite ion (NO2?). The oxygen consumption rate of the Heme/MgO with Cys was slightly higher than that of the Heme/MgO with GSH. However, a nitrosyl(protoporphyrinato)iron(II) complex produced by the Heme/MgO with GSH was lower than that produced by the Heme/MgO with Cys under the concentration of NO2? below 0.1 mmol dm?3. This result suggests that the conformational effect of thiol-compounds plays a key role on the formation of the nitrosyl(protoporphyrinato)iron(II) complex during the reduction of NO2? to nitrogen monoxide (NO). A possible mechanism for the conformational effect of GSH on the formation of the nitrosyl(protoporphyrinato)iron(II) complex is discussed, as a characteristic feature of the molecular size of GSH and an electronic interaction (repulsion) between GSH and NO2?.