Reactions of sulfur-nitrosyl iron complexes of “g = 2.03” family with hemoglobin (Hb): Kinetics of Hb-NO formation in aqueous solutions

NO-donating ability of nitrosyl [Fe-S] complexes, namely, mononuclear dinitrosyl complexes of anionic type [Fe(S2O3)2(NO)2]-(I) and neutral [Fe2(SL1)2(NO)2] with L1 = 1H-1,2,4-triazole-3-yl (II); tetranitrosyl binuclear neutral complexes [Fe2(SL2)2(NO)4] with L2 = 5-amino-1,2,4-triazole-3-yl (III); 1-methyl-1H-tetrazole-5-yl (IV); imidazole-2-yl (V) and 1-methyl-imidazole-2-yl (VI) has been studied. In addition, Roussin's “red salt” Na2[Fe2S2(NO)4]·8H2O (VII) and Na2[Fe(CN)5NO]·H2O (VIII) have been investigated. The method for research has been based on the formation of Hb-NO adduct upon the interaction of hemoglobin with NO generated by complexes I-VIII in aqueous solutions. Kinetics of NO formation was studied by registration of absorption spectra of the reaction systems containing Hb and the complex under study. For determination of HbNO concentration, the experimental absorption spectra were processed during the reaction using standard program MATHCAD to determine the contribution of individual Hb and HbNO spectra in each spectrum. The reaction rate constants were obtained by analyzing kinetic dependence of Hb interaction with NO donors under study. All kinetic dependences for complexes I-VI were shown to be described well in the frame of formalism of pseudo first-order reactions. The effective first-order rate constants for the studied reactions have been determined. As follows from the values of rate constants, the rate of interaction of sulfur-nitrosyl iron complexes (I-VI) with Hb is limited by the stage of NO release in the solution.