PubMed · 13385847
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C E LEWIS. 1956. The abnormal hemoglobin.. https://pubmed.ncbi.nlm.nih.gov/13385847/
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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] x 8H2O (VII) and Na2[Fe(CN)5NO] x 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.
The mean intrinsic thermodynamic quantity can be defined by considering the relative population of complex species in the solution and the value of intrinsic thermodynamic quantity corresponds to each step of ligation. In the present study a new method is introduced for analysis of experimental ligand binding data on basis of mean intrinsic thermodynamic quantities. In this regard, a deviation parameter was defined by comparing the non-interacting system with the cooperative interactive one. This parameter can be calculated just by estimation of the first binding constant. A set of relations between this deviation parameter and other binding characteristics, such as mean intrinsic Gibbs free energy of binding and mean Gibbs free energy of site-site interaction, have been developed. This model presents binding mechanism in a unified way that is simple, yet stringent, more straightforward, more reliable and informative. This analyzing method has been successfully applied for evaluation of various systems such as oxygen binding to hemoglobin, laurate and warfarin binding to human serum albumin, and reveals some new biological features of these binding systems.
Red blood cells (RBCs) act as O(2)-responsive transducers of vasodilator and vasoconstrictor activity in lungs and tissues by regulating the availability of nitric oxide (NO). Vasodilation by RBCs is impaired in diseases characterized by hypoxemia. We have proposed that the extent to which RBCs constrict vs. dilate vessels is, at least partly, controlled by a partitioning between NO bound to heme iron and to Cysbeta93 thiol of hemoglobin (Hb). Hemes sequester NO, whereas thiols deploy NO bioactivity. In recent work, we have suggested that specific micropopulations of NO-liganded Hb could support the chemistry of S-nitrosohemoglobin (SNO-Hb) formation. Here, by using nitrite as the source of NO, we demonstrate that a (T state) micropopulation of a heme-NO species, with spectral and chemical properties of Fe(III)NO, acts as a precursor to SNO-Hb formation, accompanying the allosteric transition of Hb to the R state. We also show that at physiological concentrations of nitrite and deoxyHb, a S-nitrosothiol precursor is formed within seconds and produces SNO-Hb in high yield upon its prompt exposure to O(2) or CO. Deoxygenation/reoxygenation cycling of oxyHb in the presence of physiological amounts of nitrite also efficiently produces SNO-Hb. In contrast, high amounts of nitrite or delays in reoxygenation inhibit the production of SNO-Hb. Collectively, our data provide evidence for a physiological S-nitrosothiol synthase activity of tetrameric Hb that depends on NO-Hb micropopulations and suggest that dysfunction of this activity may contribute to the pathophysiology of cardiopulmonary and blood disorders.