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Biomedical subjects

E Bursaux

Publications and source records attributed to E Bursaux.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1979

Interaction of butene with human hemoglobin A.

The binding of various alkanes by proteins was recognized years ago. We have studied the effect of butene (C4H8), a short-chain aliphatic hydrocarbon, on the functional properties of human adult hemoglobin. Under 1 atm pressure (100 kPa) butene decreased the affinity of hemoglobin (Hb) for oxygen (p50) by 45% without altering the cooperativity of ligand binding. This effect was independent of pH (from 7.0 to 8.0) and of ionic strength. The changes in the affinity of hemoglobin for oxygen were dependent upon the partial pressure of butene and evoked a saturating mechanism of the binding site(s). Mathematical simulation of the curve relating p50 to the concentration of dissolved butene allowed us to calculate the apparent association constants for one single binding site KHb = 10.4 mmol-1 and KHbO2 = 1.53 mmol-1 to Hb and HbO2 respectively. The larger binding of butene by Hb was confirmed by a 25% decrease in K1, the first association constant of oxygen to the tetrameric hemoglobin. It is concluded that butene is an allosteric effector of human Hb which acts most likely through hydrophobic interactions. It is postulated that the oxygen-linked binding site may be located at the alpha 1 beta 2 interface.

Alkenes↗
PubMed1979

Comparative effects of CO2 on the affinity for O2 of fetal and adult erythrocytes.

1. Oxygen-linked carbamino formation in fetal erythrocytes was compared to that measured in adult erythrocytes. 2. Whole oxygen binding curves were recorded on washed intact erythrocytes either fresh or D-glycerate-2,3-P depleted with a continuous recording technique. Erythrocytes were resuspended in buffer media of different pH and PCO2 varying from 0-10.7 kPa (80 torr) at physiological ionic strength. Oxygen linked carbamates were estimated as deltalog PO2/delta log PCO2 at constant pH and constant saturation levels from 10-90% oxygen saturation. 3. The overall CO2 effect (deltalog P50/deltalog PCO2) was consistently lower in fetal erythrocytes than in the adult. The deltalog PO2/deltalog PCO2 ratio was markedly dependent on oxygen saturation in both types of erythrocytes and highest at the early part of the oxygen binding curve. This was more so in fetal erythrocytes. 4. Carbamino formation was lower in fetal erythrocytes than in adult erythrocytes at any pH value, indicating a higher apparent pK of the alpha amino groups involved in CO2 binding in fetal erythrocytes. This may be related to the different primary structures of the non alpha chains of HbFII and HbAI. 5. The large effect of low PCO2 on both fetal and adult erythrocytes was related to the higher affinity for CO2 of deoxyhemoglobin compared to oxyhemoglobin and a model for CO2 binding analogous to that described by de Bruin et al. [6] for anion binding is proposed. 6. It is concluded that the lower CO2 binding to fetal erythrocytes is in keeping with the lower allosteric effect of other major effectors of hemoglobin within the cells. This leads to a higher affinity for O2 of fetal erythrocytes well suited for O2 transport in utero.

Adult↗
PubMed1979

The binding of lactate and chloride ions to human adult hemoglobin.

The effects of sodium lactate (Lact) on the oxygen affinity and the Bohr effect of purified human adult hemoglobin solutions have been compared to the effects of sodium chloride (Cl). Changes in the affinity for oxygen have been estimated from the variations of log(O2)50 with pH and at various salt concentration from 0.005 up to 2.0 mol.l-1. (O2)50 was calculated as alpha.P0.5 where alpha is the solubility coefficient of oxygen in the solutions at various salt concentrations. Variations of log(O2)50 with pH at constant salt concentration and variations of log(O2)50 with anion concentration at constant pH have been studied according to the linked-functions theory (Wyman, 1968). Bohr curves and salt binding curves were calculated from standard iterative curve fitting procedures and various parameters relevant to the effects of salts on hemoglobin function were estimated. It is shown that Lact and Cl increase (O2)50 and the alkaline Bohr effect in a comparable way at low salt concentration. At high concentration the effect of Lact predominated over that of Cl. The amount of oxygen linked Lact was larger than that of Cl. Binding constants for both anions to deoxy and oxy Hb were estimated. Lact and Cl have comparable binding constants to deoxy hemoglobin. By contrast Lact binds to oxy hemoglobin to a lesser extent than Cl. This may account for the differences observed in the effects of Lact and Cl on the function of hemoglobin. The reason for the low affinity of oxy hemoglobin for Lact may be related to steric differences between the two anions.

Chemical Phenomena↗
PubMed1978

Chloride binding and the Bohr effect of human fetal erythrocytes and HbFII solutions.

1. We have observed that the alkaline Bohr effect of washed human fetal erythrocytes was larger than in human adult intact red cells, in physiological conditions of pH, PCO2 and temperature. This was also observed independently of the presence of CO2 and of 2,3 diphosphoglycerate (fresh or stored erythrocytes). 2. Experiments performed in purified HbFII and HbA1 solutions and direct titration of protons released upon oxygenation confirmed the larger alkaline Bohr effect of fetal hemoglobin, at physiological ionic strength. 3. At low chloride concentration HbFII solutions had an alkaline Bohr effect identical to that measured in HbA1 solutions. 4. Titration of purified Hb solutions with increasing concentrations of NaCl evidenced a lower O2 linked chloride binding by HbFII and predominantly at acid pH. 5. It is concluded that the larger alkaline Bohr effect of fetal erythrocytes of HbFII solutions is related to a diminished acid Bohr effect, due to the lower affinity of HbFII for chloride anions. 6. The physiological interest of these results for placental O2 transfer (double Bohr effect) and O2 delivery to the foetus is discussed.

Aging↗
PubMed1978

Oxygen transport in children on maintenance haemodialysis.

1. Adaptive mechanisms of oxygen transport by blood have been studied in severely anaemic young patients on maintenance haemodialysis, in conditions of hyperphosphataemia (Pi greater than or equal to 2.2 mmol/l) or normophosphataemia. 2. In hyperphosphataemia whole-blood affinity for oxygen was slightly decreased, as measured by an increase in P50 (the partial pressure of oxygen necessary to half saturate haemoglobin). 2,3-Diphosphoglycerate was increased by 10% (P less than 0.10) whereas Pi, total erythrocyte phosphate and ATP were increased by 100%, 47% and 36% respectively, compared with control values. 3. After correction of hyperphosphataemia a small but significant decrease in P50 and 2,3-diphosphoglycerate, to normal values, was observed whereas the other variables, although significantly lowered, remained above control values. 4. In these severely anaemic and hyperphosphataemic patients P50 and 2,3-diphosphoglycerate are only slightly increased. ATP synthesis appears to be favoured over that of 2,3-diphosphoglycerate. This is possibly due to alterations in the erythrocyte membrane elicited by bi-weekly extracorporeal circulation. Adequate oxygen transport can be achieved only through a drastic increase in blood flow. Correction of hyperphosphataemia adds further to the abnormality. It is concluded that this condition could induce a long-term myocardial fatigue, which might be prevented with occasional small blood transfusions.

Adaptation, Physiological↗
PubMed1978

Hemoglobin Creteil: oxygen transport by erythrocytes. In-vitro and in-vivo studies in a high oxygen-affinity mutant hemoglobin.

Hemoglobin Hb) Creteil alpha2beta(2)89 (F5) Ser leads to Asn is a high oxygen-affinity variant that has a low cooperativity, a decreased Bohr effect, and does not interact with diphosphoglycerate (DPG) (1). This hemoglobin variant was silent by routine electrophoresis. Careful analyses of the oxygen dissociation curves of erythrocytes, determined at varying pH and Pco2 in fresh and DPG-depleted cells, gave extensive information on the abnormal function of the mutant hemoglobin. From the O2 dissociation curves of the erythrocytes of the heterozygous subject it appeared that Hb Creteil is inappropriate for O2 transport to the tissues because it remained completely saturated with O2 at normal physiologic levels of Po2. In-vivo measurements showed that only one half of the total hemoglobin present actually participated in oxygen transport. Polycythemia should therefore be maintained within clinically tolerable limits because it helps to keep arterial Po2 and Pvo2 close to their normal values and thus protects the individual from a permanent increase in blood flow.

Adult↗
PubMed1976

Renal hemodynamics and renal O2 uptake during hypoxia in the anesthetized rabbit.

The effects of hypoxic hypoxia on renal hemodynamics and metabolism have been studied in anaesthetized mechanically ventilated rabbits. Acute hypoxa (FIO2 = 0.10, PaO2 = 35 torr) induces at constant mean arterial pressure a 45% decrease in RBF, GFR, TNa and RVO2 whereas free water clearance increases. These alterations were still apparent 50 min after resuming normal arterial oxygenation. In order to assess the role of the stimulation of catecholamine release in these observations, two other sets of experiments were performed: 1) the animals were ventilated with the same hypoxic gas mixture but after alpha adrenergic blockade (phentolamine: 0.2 mg - kg - min-1 i.v.), 2) hypoxia was induced by ventilating the animals with CO (FICO = 0.002) at constnat PaO2. Increase in renal vascular resistance and reduction of renal O2 uptake were still observed. This indicates that adrenergic stimulation cannot fully explain the renal vasoconstriction encountered in hypoxia. The role of a local vasoactive factor, especially that of the renin angiotensin system is discussed. The apparent O2 cost of Na reabsorption was not greatly modified by any type of hypoxia and the Na: O2 ratio remained close to the value observed in normoxic animals. This indicates that the kidney may adapt to hypoxia by reducing its O2 demand keeping unaltered its tubular function and basal O2 needs.

Animals↗
PubMed1976

Interactions of short chain aliphatic hydrocarbons with human blood and haemoglobin A solutions.

The solubilities of methane, propane, butane and propylene were measured in human whole blood, human plasma and defatted haemoglobin solutions at 37 degrees C. For these four hydrocarbons the solubility coefficient (alpha = ml of gas STPD dissolved in one mal of the solvent under a pressure of one atmosphere) is higher in plasma than in an isoosmolar aqueous solution and higher in whole blood than in plasma. This is due to the presence of proteins and particularly of haemoglobin as shown by the dependence of alpha upon the concentration of haemoglobin in the medium. O2 capacity of human blood is not altered in the presence of these hydrocarbons and its affinity for O2 is slightly decreased.

Air Pollutants↗
PubMed1975

The bone CO2 compartment: evidence for a bicarbonate pool.

CO2 was measured in rat cortical bone samples with an accurate manometric technique. Bone CO2 content increased with the age of the animals. When heated to constant weight, bone samples lost 15.5% of their initial fresh CO2 content, indicating that CO2 exists in several chemical forms in the bone CO2 pool. Bone samples were exposed in vitro to atmospheres of increasing PCO2. Bone CO2 increased by 15% of its original content when exposed for 60 min. to pure CO2. CO2 uptake by bone in vitro was shown to be time- and PCO2-dependent, evoking a saturating mechanism and requiring the presence of water in bone. These findings lead to the conclusion that the bone CO2 compartment consists of 30% bicarbonate and 70% carbonate. The exact location of the bicarbonate pool and its availability as a buffer store for the whole organism are discussed.

Animals↗
PubMed1975

The exchange of bone CO2 in vivo.

Bone 14CO2 specific activities have been measured in 10 male rats perfused for 30, 60 or 120 minutes with [14C]bicarbonate. A steady blood 14CO2 specific activity is observed from the 30th minute, whereas bone 14CO2 specific activity increased linearly with time. About 7-10% of the total activity infused may be recovered in the skeleton at any given time. Bone samples heated to constant weight lost 15% of their total CO2 content and more than 50% of the 14CO2 activity. This indicates that 14CO2 present in bone is almost exclusively located in a bicarbonate pool which may be considered as the rapidly exchangeable bone CO2 fraction. The rate of exchange between bone and blood CO2 is estimated at a maximum of 15% of the total CO2 production. It is postulated that blood flow to the skeleton is the limiting factor for bone CO2 exchange. These results lead to the conclusion that the large bone CO2 store cannot play a significant role in the buffering of extracellular fluids in acute acid-base abnormalities.

Animals↗
PubMed1975

[Affinity of hemoglobin for oxygen and tolerance to hypoxia].

The transfer of O2 in the system between the lung captation and the delivery to tissues is insured by a whole of factors that are components of Fick's equation. The two most important in this O2 transfer are heart output and blood concentration in hemoglobin (transfer capacity of O2). The affinity of blood for O2, evaluated by the determination of P50 (PO2 of half saturation of Hb) interfers also, but we have till presently no precision for what concerns its relative importance. Two demonstrative situations of chronic hypoxia are taken in consideration: adaptation to high altitude hypoxia and the reaction of the system to hypoxia in chronic respiratory deficiency. The influence of displacements of the dissociation curve of HbO2 (Bohr effect, variation in the erythrocytary DPG) is object of discussion. Authors insist particularly on the fact that the fall in the affinity of Hb for O2 (increase in P50) is not always a beneficial mechanism for the delivery of O2 to tissues, particularly in the case of severe hypoxia.

Altitude↗