Oxygen affinity

Ebook "Thom H. Dunning, Jr.: A festschrift from theoretical chemistry accounts" provides valuable content for all researchers in theoretical chemistry and will especially benefit those research groups and libraries with limited access to the journal. Originally published in the journal Theoretical Chemistry Accounts, these outstanding contributions are now available in a hardcover print format, as well as a special electronic edition.

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Approximately 90 haemoglobinopathies have been identified that result in abnormally high oxygen affinity. One of these is haemoglobinopathy York (HbY), first described in 1976. HbY causes an extreme leftward shift of the oxygen dissociation curve with the P50 value changing to 12.5 - 15.5 mmHg (normal value 26.7 mmHg), indicating that approximately half of the haemoglobin is not available as oxygen carrier.

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Even extremely high-doses of the potent opioid, sufentanil, cannot reliably suppress stress responses to intense surgical stimuli such as sternotomy. The chemically related opioid remifentanil with its different pharmacokinetics and binding affinities for delta- and kappa-opioid receptors might be more effective in attenuating these responses.

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The effects of ionic strength and temperature on the dissociation constants of adefovir (PMEA) and cidofovir (HPMPC) used as antiviral drugs were studied at 298 K, 308 K, and 318 K in aqueous media and at different ionic strength backgrounds of NaCl potentiometrically. The dissociation constants of the ligands were determined via the calculation of the titration data with the SUPERQUAD computer program. The thermodynamic parameters (∆G, ∆H , and ∆S) for all species were calculated.

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A granulated type of commercial activated carbon (GAC) with surface area of 828 m2/g was treated with a strong solution of sulfuric acid (98% wt.) at a temperature of 30°C. The physicochemical and porous properties and the surface chemistry of the sorbents were investigated and compared in detail. It was established that the lower temperatures of impregnation and the higher concentration of H2SO4 solution resulted in the introduction of higher percentages of sulfur-containing groups and smaller porosity loss.

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In this chapter you will learn: Structure of myoglobin and hemoglobin similar; understand oxygen binding curves (where high and low affinity binding occurs); understand positive cooperatively in relationship to oxygen binding to hemoglobin, be able to describe this in relationship to protein conformation and the sigmoidal oxygen binding curve; be able to describe T and R conformations of Hb; understand how oxygen binding changes Hb conformation; define allosteric interaction;...

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This paper reports the results obtained using the osmotic stress method applied to the purified cathodic and anodic hemoglobins (Hbs) from the catfishHoplosternum littorale, a species that displays facultative accessorial air oxygen-ation. We demonstrate that water potential affects the oxy-gen affinity ofH. littoraleHbs in the presence of an inert solute (sucrose). Oxygen affinity increases when water activity increases, indicating that water molecules stabilize thehigh-affinitystateof theHb.

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The different effects of pH and NaCl on individual O2-binding properties ofaandbsubunits within liganded tetramer and dimer of human hemo-globin (HbA) were examined in a number of laser time-resolved spectro-scopic measurements. A previously proposed approach [Dzhagarov BM & Lepeshkevich SV (2004)Chem Phys Lett390, 59–64] was used to determine the extent of subunit dissociation rate constant difference and subunit affinity difference from a single flash photolysis experiment.

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Branchiopod crustaceans are endowed with extracellular, high-molecular-mass hemoglobins (Hbs), the functional and allosteric properties of which have largely remained obscure. The Hb of the phylogenetically ancientTri-ops cancriformis(Notostraca) revealed moderate oxygen affinity, coopera-tivity and pH dependence (Bohr effect) coefficients: P50¼13.3 mmHg, n50¼2.3, andu¼)0.18, at 20C and pH 7.44 in Tris buffer. Thein vivo hemolymph pH was 7.52.

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Evidence is accumulating that oxygen access in proteins is guided and con-trolled. We also have recently described channels that might allow access of oxygen to pockets at the active site of the flavoproteinD-amino acid oxi-dase (DAAO) that have a high affinity for dioxygen and are in close prox-imity to the flavin.

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Figure 101-1 RBC metabolism. The Embden-Meyerhof pathway (glycolysis) generates ATP for energy and membrane maintenance. The generation of NADPH maintains hemoglobin in a reduced state. The hexose monophosphate shunt generates NADPH that is used to reduce glutathione, which protects the red cell against oxidant stress. Regulation of 2,3-bisphosphoglycerate levels is a critical determinant of oxygen affinity of hemoglobin.

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Low-affinity hemoglobins should be considered in patients with cyanosis or a low hematocrit with no other reason apparent after thorough evaluation. The P 50 test confirms the diagnosis. Counseling and reassurance are the interventions of choice. Methemoglobin should be suspected in patients with hypoxic symptoms who appear cyanotic but have a Pa O2 sufficiently high that hemoglobin should be fully saturated with oxygen.

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Unstable hemoglobins occur sporadically, often by spontaneous new mutations. Heterozygotes are often symptomatic because a significant Heinz body burden can develop even when the unstable variant accounts for a portion of the total hemoglobin. Symptomatic unstable hemoglobins tend to be β-globin variants, because sporadic mutations affecting only one of the four α-globins would generate only 20–30% abnormal hemoglobin. Hemoglobins with Altered Oxygen Affinity High-affinity hemoglobins [e.g.

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The homozygous state for the α-thalassemia-1 cis deletion (hydrops fetalis) causes total absence of α-globin synthesis. No physiologically useful hemoglobin is produced beyond the embryonic stage. Excess γ-globin forms tetramers called Hb Barts (γ4), which has a very high oxygen affinity. It delivers almost no O 2 to fetal tissues, causing tissue asphyxia, edema (hydrops fetalis), congestive heart failure, and death in utero. α-Thalassemia-2 trait is common (15–20%) among people of African descent. The cis α-thalassemia-1 deletion is almost never seen, however.

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Hemoglobin-oxygen dissociation curve. The hemoglobin tetramer can bind up to four molecules of oxygen in the iron-containing sites of the heme molecules. As oxygen is bound, 2,3-BPG and CO2 are expelled. Salt bridges are broken, and each of the globin molecules changes its conformation to facilitate oxygen binding. Oxygen release to the tissues is the reverse process, salt bridges being formed and 2,3-BPG and CO2 bound. Deoxyhemoglobin does not bind oxygen efficiently until the cell returns to conditions of higher pH, the most important modulator of O2 affinity (Bohr effect).

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Classes There are five major classes of hemoglobinopathies (Table 99-1). Structural hemoglobinopathies occur when mutations alter the amino acid sequence of a globin chain, altering the physiologic properties of the variant hemoglobins and producing the characteristic clinical abnormalities. The most clinically relevant variant hemoglobins polymerize abnormally, as in sickle cell anemia, or exhibit altered solubility or oxygen-binding affinity. Thalassemia syndromes arise from mutations that impair production or translation of globin mRNA, leading to deficient globin chain biosynthesis.

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