Studies on nitrosyl hemes in Ni(II)-Fe(II) hybrid hemoglobins.
TL;DR: The bond between N(epsilon) and Fe is fundamental to the structure-function relation in Hb, as the motion of this nitrogen triggers the vast transformation, which occurs in the whole molecule on attachment of NO.
About: This article is published in Nitric Oxide.The article was published on 2005-12-01. It has received 2 citations till now.
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TL;DR: It is demonstrated that ·SHb(II)NO is formed and that it has the EPR spectrum expected for NO bound to the heme in the β-chain plus that of a thiyl radical.
Abstract: The reduction of nitrite by deoxygenated hemoglobin chains has been implicated in red cell-induced vasodilation, although the mechanism for this process has not been established. We have previously demonstrated that the reaction of nitrite with deoxyhemoglobin produces a hybrid intermediate with properties of Hb(II)NO+ and Hb(III)NO that builds up during the reaction retaining potential NO bioactivity. To explain the unexpected stability of this intermediate, which prevents NO release from the Hb(III)NO component, we had implicated the transfer of an electron from the β-93 thiol to NO+ producing ·SHb(II)NO. To determine if this species is formed and to characterize its properties, we have investigated the electron paramagnetic resonance (EPR) changes taking place during the nitrite reaction. The EPR effects of blocking the thiol group with N-ethyl-maleimide and using carboxypeptidase-A to stabilize the R-quaternary conformation have demonstrated that ·SHb(II)NO is formed and that it has the EPR spectrum e...
18 citations
TL;DR: An overview of interactions between Hb (modified or not) and EC is presented and a wide range of techniques and methods to assess oxidative stress and inflammation responses of EC after exposure to Hb are proposed to serve as a guide to evaluate in vitro toxicity of new Hb molecules.
Abstract: The most common and widely transplanted tissue worldwide is blood. But concerns about safety and adequacy of blood transfusion have fostered 20 years of research into blood substitutes such as oxyg...
4 citations
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TL;DR: The oxygenation of haemoglobin is accompanied by structural changes in the subunits triggered by shifts of the iron atoms relative to the porphyrin and, in the β-subunits, also by the steric effect of oxygen itself.
Abstract: The oxygenation of haemoglobin is accompanied by structural changes in the subunits triggered by shifts of the iron atoms relative to the porphyrin and, in the β-subunits, also by the steric effect of oxygen itself. The oxygen-free form is constrained by salt-bridges which are broken by the energy of haem–haem interaction with the release of H+. 2,3-Diphosphoglycerate may add to the constraints by being stereochemically complementary to a site between the β-chains ; this complementarity is lost on oxygenation.
2,625 citations
TL;DR: Using a novel procedure, the enzyme has been purified to homogeneity from bovine lung with a heme content of approximately 1 heme/heterodimer, and .NO increases the Vmax of sGC by 100-200-fold, probably by interacting with aHeme moiety on the enzyme.
Abstract: Nitric oxide (.NO) is a recently discovered signaling agent which plays a role in many biological processes such as vasodilation and neuronal synaptic transmission. The only receptor characterized thus far for .NO is the soluble form of guanylate cyclase (sGC). .NO increases the Vmax of sGC by 100-200-fold, probably by interacting with a heme moiety on the enzyme. Although several procedures exist for purifying sGC, these procedures result in preparations with low heme contents. Using a novel procedure, the enzyme has been purified to homogeneity from bovine lung with a heme content of approximately 1 heme/heterodimer. The UV-visible spectrum of the enzyme contains a Soret peak centered at 431 nm and a single broad alpha/beta peak at 555 nm indicative of a 5-coordinate ferrous heme with histidine as the axial ligand. The heme moiety does not bind oxygen but will readily bind .NO to form a 5-coordinate complex or carbon monoxide (CO) to form a 6-coordinate complex. Oxidation of the heme with ferricyanide shifts the Soret to 393 nm, due most likely to the formation of a 5-coordinate ferric heme. In the ferric state, the heme will apparently not bind water but will bind cyanide with reduced affinity compared to methemoglobin and metmyoglobin. Purified enzyme containing 1 heme/heterodimer is activated 130-fold by .NO and 4.4-fold by CO.
639 citations
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01 Jan 1990TL;DR: Allosteric membrane proteins are studied as indicators of allosteric equilibrium on spin state and coordination of the haem iron and of feedback inhibition without change of quaternary structure in E. Coli repressors.
Abstract: Preface 1. Introduction 2. Haemoglobin: Dependence of allosteric equilibrium on spin state and coordination of the haem iron 3. Haemocyanin: Dependence of allosteric equilibrium on coordination and valency of a binuclear copper complex 4. Haemerythrin: Cooperativity in a binuclear iron complex 5. Glycogen phosphorylase: Control of glycolysis 6. Phosphofructokinase: Further control of glycolysis 7. Feedback inhibition of a biosynthetic pathway: Aspartate Transcarbamoylase 8. Control of nitrogen metabolism: Glutamine synthetase 9. Cooperativity and feedback inhibition without change of quaternary structure: The "trp" and "met" repressors of E. Coli 10. Immunoglobulins: Cooperative binding to multivalent antigens 11. Allosteric membrane proteins.
548 citations
429 citations
TL;DR: EPR parameters of nitric oxide complexes of ferrous hemoproteins are not significantly affected by substitutions of two vinyl groups at positions 2 and 4 of the porphyrin ring with two ethyl groups (mesoheme) or hydrogens (deuteroheme), indicating that the nucleophilicity of porphirin side chains has no appreciable effect on the metal-ligand bond strength.
331 citations