Abstract
Abstract We have investigated the reaction between the system of hydroxo(protoporphyrinato)iron(III) (Heme) complex adsorbed on magnesium oxide (MgO) powder in the presence of cysteine (Cys) (Heme/MgO/Cys) and the nitrite ion (NO2−), using a Clark-type oxygen electrode and an ESR method. The nitrite ion acted as an inhibitor on the oxygen consumption by the Heme/MgO/Cys. This inhibition was not observed on the system of Heme aqueous solution (Hemeaq) in the presence of cysteine (Hemeaq/Cys) and NO2−, where the oxygen consumption was caused. The formation of a nitrosyl(protoporphyrinato)iron(II) complex in the reaction mixture of the Heme/MgO/Cys and NO2− was confirmed by the measurement of an ESR spectrum. This result suggests that the formation of the nitrosyl(protoporphyrinato)iron(II) complex during the reduction of NO2− to nitrogen monoxide (NO) plays a key role on the inhibitory action of NO2−. A possible mechanism for the formation of the nitrosyl(protoporphyrinato)iron(II) complex on the reaction between the Heme/MgO/Cys and NO2− is discussed, as a characteristic feature of our heterogeneous system.
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