Jane M. Heim

Detection, formation, and relevance of hemichromes and hemochromes.

Publisher Summary Native hemoglobins contain one histidine coordinated to the iron on the proximal side of the heme and another histidine in the ligand pocket on the distal side of the heme. Oxygen located in this pocket in oxyhemoglobin can be replaced by other neutral ligands, such as carbon monoxide, nitric oxide, and alkylisocyanide in the reduced Fe(II) hemoglobins. The iron in deoxyhemoglobin is in a high-spin state, whereas all of the Fe(II) complexes are in a low-spin state. Oxidized Fe(III) hemoglobin ligands bound in this pocket include water, hydroxide, fluoride, azide, thiocyanate, imidazole, and cyanide. The spin state for these complexes depends on the strength of the axial ligand and can be high spin (example, fluoride), low spin (example, cyanide), or a mixture (example, hydroxide). Low-spin hemoglobin complexes also exist when the exogenous ligand is replaced by an endogenous amino acid side chain. These low-spin complexes define the Fe(II) hemochromes and Fe(III) hemichromes. For many other heme proteins, low-spin complexes involving axial coordination of two amino acid side chains are functional. This chapter discusses the methods for determining the presence of the low-spin complexes. The characterization of different types of hemichromes, primarily on the basis of electron paramagnetic resonance (EPR) is reviewed. The chapter discusses the different ways of forming hemi(hemo)chromes. The processes clearly dissociated with denaturation to those clearly indicative of native substates and the significance of hemi(hemo)chrome formation are also discussed. The information regarding hemoglobin that can be obtained from studies of hemi(hemo)chrome formation and the possible functional role of bis-histidine complex formation have also been described in the chapter.

Interaction of metal ions with polynucleotides and related compounds. XX. Control of the conformation of polyriboadenylic acid by divalent metal ions

Abstract Divalent metal ions have profound effects on the conformation of poly A, as indicated by changes in optical rotatory dispersion and ultraviolet spectra, with different metal ions having distinctly different effects. At pH 6 and in the presence of 5 × 10 −2 M NaCl, two moles Ni(II) or Co(II) per mole of poly A residue stabilize the single helix; the same amount of Mg(II), Ca(II), Zn(II) or Mn(II) produce a mixture of double and single helix, while Cu(II) and Cd(II) induce the formation of a random coil structure. Under other conditions, these same metals have different effects, with the amount of added NaCl an important factor that can be used to control the way in which a particular divalent metal ion will induce the transition from a double helix to single helix or from helix to coil. The single helix is stabilized by metals binding to phosphate; the double helix is destabilized by metal ions binding to either phosphate or base, the former producing single helix and the latter random coil. The melting temperature of double helical poly A is diminished when metal ions bind to either type of site.

THE ROLE OF HEMOGLOBIN IN GENERATING OXYRADICALS

The largest fraction of dioxygen in mammalian systems is associated with hemoglobin. The primary function of hemoglobin is the transport of oxygen from the lungs to the tissues, which requires reversible oxygen binding. Nevertheless, a slow rate of autoxidation does take place. It has furthermore been demonstrated that autoxidation coincides with the formation of superoxide.1,2

Impaired Hemorheology in the Aged Associated with Oxidative Stress

Oxygen transport to the tissues depends on the ability of blood cells to flow through the circulatory system. The flow of blood in the circulatory network depends upon many factors. The viscosity which measures the resistance to flow is a major factor in determining the hemorheological properties of blood. A number of studies (Torre la de et al.; 1993, Paul et al., 1996; Sharp et al., 1996) indicate that the hemorheological properties, which determine blood flow, are impaired in the aged. Thus, aging has been shown to be associ ated with an increase in fibrinogen, plasma viscosity, whole blood viscosity and whole blood filterability (Avellone et al., 1993, Lechner et al., 1987).

The effect of divalent ions on the isolation of proteins from rat liver nucleoprotein

Abstract The nature and quantity of acid-soluble proteins separated from rat liver nucleoprotein is greatly dependent upon the presence of divalent metal ions. In the absence of these ions, and particularly in the presence of EDTA, low yields of protein are obtained because of greater solubility of the nuclear contents. Moreover, the use of EDTA selectively removes the “arginine-rich” proteins from the nucleoprotein pellet, so that eventual protein fractionation results in relatively extensive retention of “arginine-poor” proteins. The use of divalent metal ions (Mg 2+ , Mn 2+ ) produces similar fractionation patterns. The use of NaCl as the electrolyte allows the isolation of some arginine-rich protein, but in very low yield when compared to the preparations using divalent ions. Thus, ionic strength is a minor factor in the extraction of the arginine-rich proteins from such nuclei, but the presence of divalent metal ions is the most important requirement. Evidently these metal ions exercise an important role in maintaining the structural integrity of arginine-rich nucleoproteins in the nuclei.

Effects of aging on the lipid order and composition of rat adipocyte ghosts

An analysis of the cholesterol/phospholipid ratio of adipocyte ghosts from rat epididymal fat pads shows a significant increase with age (P less than 0.005). An attempt to correlate these changes with the order of the lipid matrix was made using the stearic acid spin label 2-(3-carboxypropyl)-4, 4-dimethyl-2-tridecyl-3-oxazolidinyloxyl [I(12,3)]. Although order was negatively correlated with temperature in preparations from both 6- and 24-month-old rats, no effect of age could be detected.