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C Poyart

Publications and source records attributed to C Poyart.

At least 163 records · Page 9Linked to original sources
PubMed1984

Structure and function of Hb Saint-Jacques (alpha 2 beta 2 140 (H18) Ala----Thr): a new high-oxygen-affinity variant with altered bisphosphoglycerate binding.

A low P50 value in a fresh red blood cell suspension was discovered in a polycythemic patient (Hb 19 g X dl-1). Routine acid and alkaline electrophoreses of the hemolysate were identical to normal hemolysate. Isoelectrofocusing (pH gradient 6-8) did not reveal any abnormal band whether performed with the fully liganded or deoxygenated samples. Precise analyses of the oxygen dissociation curves of the propositus' red cells demonstrated a biphasic Hill plot, a normal Bohr effect and low interaction with 2,3-bisphosphoglycerate (2,3-DPG). Studies on the unfractionated hemolysate confirmed these observations and the inhibition of the effect of organic phosphates. Structural studies were carried out on the mixture of beta A + beta X chains and revealed the presence of two beta Tp14 peptides. Sequencing the abnormal beta Tp14 peptide showed the substitution Ala----Thr of the beta 140 (H18) residue. This new variant was named Hb Saint-Jacques. Examination of the three dimensional model of HbAo indicates that the substitution beta 140 (H18) Ala----Thr induces van der Waals interactions with the nearby lysine-82 (EF6) and leucine-81 (EF5) and a displacement of the EF corner of the beta chains. This is likely to change the normal position of the lysine-82 (EF6), a major anionic binding site in the central cavity between the two beta chains. Functional studies confirm the interpretation of a steric hindrance inhibiting the binding of large organic phosphates to Hb Saint-Jacques.

2,3-Diphosphoglycerate↗
PubMed1984

A new hemoglobin variant altering the alpha 1 beta 2 contact: Hb Chemilly alpha 2 beta 2 99(G1)Asp leads to Val.

Hemoglobin Chemilly (alpha 2 beta 2 99(G1)Asp leads to Val), a high oxygen affinity variant, was uncovered in the red blood cells of a polycythemic patient who reported to the hospital concerning periodic headaches. We describe the molecular abnormality and functional studies of this new abnormal Hb. beta 99(G1)Asp, an invariant residue of hemoglobin, is considered a key amino acid for conformational changes between the R in equilibrium T quaternary structures responsible for the allosteric behavior of hemoglobin. Hb Chemilly exhibits a high O2 affinity, very low cooperativity and reduced Bohr effect. Its functional abnormalities are compared to the 5 other Hb variants at site beta 99(G1) described up to now of the 7 single base substitutions predictable from the genetic code.

Adult↗
PubMed1984

[Erythrocytosis due to a high-affinity hemoglobulin: mutant hemoglobin Saint-Jacques beta 140 (H18) Ala----Thr with a change in the 2,3-diphosphoglycerate binding site].

All the high oxygen affinity variants have substitutions in regions that are crucial to hemoglobin function: mainly the alpha 1 beta 2 interface, the C-terminal end of the beta chain and the aminoacid residues involved in the 2,3 disphophoglycerate (2,3 DPG) binding site. In this report we describe a new variant with familial erythrocytosis: hemoglobin Saint-Jacques beta 140 (H18) Ala----Thr, whose main abnormality is a defect in organic phosphate binding in the central cavity between to two beta chains. This variant could not be separated from hemoglobin A by standard electrophoretic methods or by isoelectric focusing. The abnormal peptide was isolated by reverse-phase high performance liquid chromatography and the structural modification determined by manual sequencing micro-method. Functional studies on red blood cells as well as on stripped lysate showed increased oxygen affinity, normal Bohr effect, decreased heme-heme interaction and loss of the 2,3 DPG regulatory effect.

2,3-Diphosphoglycerate↗
PubMed1983

Spectral evidence for sub-picosecond iron displacement after ligand detachment from hemoproteins by femtosecond light pulses.

We have measured spectral and kinetic differences in protoheme, sperm whale or horse heart myoglobin and human hemoglobin following photodissociation induced by optical pulses of 80 fs duration. Full ligation was performed with oxygen or carbon monoxide. Femtosecond kinetics and transient difference spectra revealed the appearance of a deoxy species with tau approximately equal to 250-300 fs. The transient deoxy species in myoglobin and hemoglobin evidenced a 3-4 nm red shift of their delta A spectra compared with the equilibrium delta A spectrum. This shift was not observed after photodissociation of the carbon monoxide liganded protoheme. We proposed that the 250 fs time constant corresponding to the appearance of the deoxy-like species is related to the displacement of the ferrous iron out of the heme plane. Consequently, the small red shift of the delta A spectra observed in photodissociated hemoproteins may be tentatively attributed to changes in the vibrational modes of either the proximal histidine-Fe2+ bond and/or of the N4 porph-Fe-N epsilon His (F8) bent.

Animals↗
PubMed1983

Femtosecond photolysis of CO-ligated protoheme and hemoproteins: appearance of deoxy species with a 350-fsec time constant.

Photolysis of HbCO, MbCO, and CO-protoheme has been investigated by measuring transient differential spectra and kinetics of induced absorption after excitation with a 250-fsec laser pulse at 307 nm. Probing was performed by a part of a continuum pulse between 395 and 445 nm. Photodissociation of the three liganded species occurred within the pulse duration. By contrast, the formation of deoxy species appeared with a mean (+/- SD) response time of 350 +/- 50 fsec. This time constant was identical for the three species and independent of the presence or absence of the protein structure. Our results suggest the formation of a transient high-spin in plane iron (II) species which relaxes in 350 fsec to a high-spin stable state with concerted kinetics of CO departure and iron displacement. The spin transition is suspected to occur via liganded excited states which relax in part to non-reactive states with a 3.2-psec time constant.

Carbon Monoxide↗
PubMed1982

Temperature independence of the alkaline Bohr effect in pig red cells and pig haemoglobin solutions.

The influence of temperature on the oxygen affinity and the alkaline Bohr effect of pig red cells and pig hemoglobin solutions has been compared to that of human adult red cells and human adult hemoglobin. Pig red cells and pig Hb evidence a lower affinity for oxygen in various conditions of pH, temperature and salt concentration, in the presence as well as in the absence of organic phosphates. It has been observed that the alkaline Bohr effect of pig Hb was reduced by 20-25% compared to Hb A0 and independent of changes in temperature, contrary to human Hb A0. Titrations of pig Hb with C1- indicate a lower heterotropic effect of this anion at low concentration of the salt. It is concluded that this may be the origin of the temperature independence of the alkaline Bohr effect in pig Hb. Conversely, the temperature dependence of the alkaline Bohr effect of Hb A0 should be related to the oxygen-linked binding of C1- at the alpha 1-alpha 2 interface.

Adult↗
PubMed1982

Effect of carbamination on the buffering power of purified human hemoglobin A solutions at two temperatures.

The effect of CO2 on hemoglobin buffering power was studied in purified human hemoglobin A solutions, native and specifically carbamoylated on N-terminal valines, at 26 degrees C and 42 degrees C, in the oxy and deoxy states. Titrations were performed by varying Pco2 and by strong acid or base in the absence of CO2. The participation of N-terminal valines to the total buffering power was estimated by subtracting the buffering value measured on carbamoylated hemoglobin solutions from that measured on native hemoglobin solutions. In the absence of CO2 the buffering value of native and modified hemoglobin increased slightly (less than 10%) (a) on going from the deoxy to the oxy state, and (b) on raising the temperature from 26 degrees C to 42 degrees C. In the presence of CO2 the buffering value of Hb increased from 9.1 to 16.6 mol mol Hb4-1 pH-1 and that of HbO2 from 10.1 to 19.6 mol mol Hb4-1 pH-1 when the temperature was raised from 26 degrees C to 42 degrees C. These figures correspond to a rise in the fraction of the total buffering value attributable to N-terminal valines from 11% to 25% for Hb and from 3% to 33% for HbO2. The present results point to a non-specific effect of CO2 within the hemoglobin molecule independent of that of N-terminal valines. This effect nearly doubles the buffering value for CO2 when the temperature is raised, and contributes to pH regulation and CO2 removal in tissues with a high metabolic rate.

Buffers↗
PubMed1981

[Structural basis for the functional properties of hemoglobin (author's transl)].

Functional properties of tetrameric HbA are schematically described in this short review. After considering the various structures of the protein and its binding with heme, an attempt is made to explain the influence of this structure on the affinity of Hb for oxygen, cooperative binding of oxygen, and the alkaline Bohr effect. Fixation of erythrocytic anions (chlorine and 2,3 diphosphoglycerate) modulate certain intrinsic properties, allowing the Hb molecule to provide for efficacious transport of oxygen between the environment and the metabolically active tissues.

Amino Acids↗
PubMed1981

Hemoglobin Barcelona beta 94 (FG1) Asp leads to His : a new hemoglobin Variant with increased oxygen affinity.

A new variant, Hb Barcelona (beta 94 Asp leads to His) found in a Spanish family presenting with a mild polycythemia, is described. Its increase in oxygen affinity is explained by the rupture of the salt-bridge between beta 94 Asp and beta 146 His which normally stabilizes the deoxystructure and accounts for approximately half of the Bohr effect. A comparison between the estimated oxygen transport to the tissues by the blood from a patient with Hb Kempsey and that of the patients with Hb Barcelona showed, in the latter cases, that an almost normal oxygen delivery was obtained by the increase of the hemoglobin level.

Chemical Phenomena↗
PubMed1980

The involvement of tertiary conformational changes and the role of the alpha-chain-binding sites on oxygen-linked chloride release from human hemoglobin.

Chloride anions, when bound to human hemoglobin, lower the affinity for oxygen and increase the alkaline Bohr effect. These oxygen-linked characteristics are attributed to the preferential binding of Cl- to both alpha- and beta-chains in their deoxy configuration. It is demonstrated that the release of Cl- upon oxygenation is mainly due to tertiary changes, as shown by the effect of the anion on K1, the affinity constant of hemoglobin for oxygen at a very low saturation level (y less than or equal to 1.5%) where the cooperativity is unity. Investigation of the chloride effect on adult hemoglobin specifically carbamylated at the N-terminal valine of the alpha-chains, indicated a large inhibition of the effect of Cl-. The alpha-chain-binding sites appear to be the sites of the greatest affinity for the anion.

Binding Sites↗
PubMed1980

Structural and functional studies of hemoglobin Suresnes (arg 141 alpha 2 replaced by His beta 2). Consequences of disrupting an oxygen-linked anion-binding site.

Hb Suresnes is a human hemoglobin variant in which histidine replaces arginine at the COOH terminus of the alpha chains. The COOH-terminal arginines of the alpha chains play a major role in normal human hemoglobin (HbA), both by electrostatic interactions which constrain deoxygenated hemoglobin in a low affinity quaternary conformation and by involvement in oxygen-linked anion binding knoiwn to give rise to a large part of the alkaline Bohr effect. An x-ray crystallographic analysis of deoxyHb Suresnes reveals the loss of the normal intersubunit salt bridge to lysine 127 alpha and a decrease in the occupancy of inorganic anions at the alpha chain aniom-binding site. Relative to normal HbA, Hb Suresnes has a high affinity for oxygen, a reduced cooperativity in oxygen biding, and greatly reduced pH and chloride sensitivity. similar changes are found in carboxypeptidase B-digested hemoglobin Ao where the COOH-terminal arginine is removed by enzymatic digestion. Both equilibrium and kinetic manifestations of the destabilization of the normal low affinity configuration are observed. Inositol hexaphosphate restores cooperativity and pH sensitivity but, even in the presence of this strong allosteric effector, the low and high affinity conformations of Hb Suresnes appear to differ from those of HbA. In both the unliganded and liganded states, apreciable subunit dissociation of Hb Suresnes is apparent, which suggests that the substitution disrupts bonds which normally stabilize the tetramer. Structural changes at both the quaternary and tertiary level appear to contribute to alterations in the high and low affinity conformations of ths abnormal hemoglobin. Hb Suresnes thus illustrtaes the consequences of the loss of an important oxygen-linked anion-binding site.

Anions↗
PubMed1980

Oxygen-linked binding of halothane to human adult haemoglobin.

The affinity for oxygen of normal human haemoglobin (Hb) solutions was measured in the presence of increasing concentrations of halothane. We observed a maximum increase in P50 of 25% with halothane 40 kPa compared with control (oxygen-argon gas mixtures) indicating the oxygen-linked character of the binding of halothane to the Hb molecule. The effect of halothane on P50 was independent of pH between 7.0 and 8.0 and of chloride concentration between 10 and 100 mmol litre-1. This suggests that halothane-Hb interactions may occur through hydrophobic linkage as occurs with short chain aliphatic hydrocarbons. The oxygen-linked binding of halothane appears of minor importance in altering oxygen binding to Hb in vivo compared with other factors such as chloride ion or 2, 3-DPG.

Adult↗
PubMed1980

[Possible contribution of amino-acids in myocardium response to hypoxia (author's transl)].

The purpose of the present report is to review current knowledge on amino-acid metabolism during hypoxia in vivo and in vivo, mainly in the myocardium. We have first considered biochemical events occurring in muscles during anoxia either in facultative anaerobic invertebrates or in aerobic vertebrates. In the invertebrate muscle, simultaneous utilization of carbohydrate and amino acids in anoxia leads to ATP formation and accumulation of CO2, alanine and succinate. In aerobic species, ATP production in anoxic conditions is mostly or totally derived from glycolysis, lactate being the end product. Recent studies from various authors have suggested that amino acid utilization may be present in aerobic species exposed to hypoxia and contribute to energy production under these conditions. Experiments using the isolated rat heart preparation have demonstrated the accumulation of alanine and succinate in addition to that of lactate during short period of hypoxia (Fig. 8). The relative importance of these biochemical events in term of energy production is discussed. It is also postulated that the accumulation of alanine and succinate in the myocardium during hypoxia may be involved in other physiological processes.

Aerobiosis↗