Presence Of DPG Research Articles

Application of Dispersed Particle Gel to Inhibit Surfactant Adsorption on Sand

AbstractThis article highlights an efficient and cost‐effective additive‐dispersed particle gel (DPG) to reduce surfactant adsorption on sand. Indoor experiments were conducted to study the effect of DPG on static adsorption and dynamic adsorption of the surfactant. The static adsorption data were evaluated using different isotherm models and the Redlich–Peterson isotherm matched the best. Results showed a significant inhibition of surfactant adsorption in the presence of DPG. The dynamic adsorption of SDS on sand decreased to 0.78, 0.68 and 0.61 mg/g compared with original value of 1.17 mg/g by adding 0.1, 0.2 and 0.3 wt% DPG particles, respectively. This study suggests that DPG can inhibit the adsorption of surfactant on sand effectively.

Insulin Action on Polyunsaturated Phosphatidic Acid Formation in Rat Brain: An “In Vitro” Model with Synaptic Endings from Cerebral Cortex and Hippocampus

The highly efficient formation of phosphatidic acid from exogenous 1-stearoyl-2-arachidonoyl-sn-glycerol (SAG) in rat brain synaptic nerve endings (synaptosomes) from cerebral cortex and hippocampus is reported. Phosphatidic acid synthesized from SAG or 1,2-dipalmitoyl-sn-glycerol (DPG) was 17.5 or 2.5 times higher, respectively, than from endogenous synaptosomal diacylglycerides. Insulin increased diacylglycerol kinase (DAGK) action on endogenous substrate in synaptic terminals from hippocampus and cerebral cortex by 199 and 97%, respectively. Insulin preferentially increased SAG phosphorylation from hippocampal membranes. In CC synaptosomes insulin increased phosphatidic acid (PA) synthesis from SAG by 100% with respect to controls. Genistein (a tyrosine kinase inhibitor) inhibited this stimulatory insulin effect. Okadaic acid or cyclosporine, used as Ser/Threo protein phosphatase inhibitors, failed to increase insulin effect on PA formation. GTP gamma S and particularly NaF were potent stimulators of PA formation from polyunsaturated diacylglycerol but failed to increase this phosphorylation when added after 5 min of insulin exposure. GTP gamma S and NaF increased phosphatidylinositol 4,5 bisphosphate (PIP2) labeling with respect to controls when SAG was present. On the contrary, they decreased polyphosphoinositide labeling with respect to controls in the presence of DPG. Our results indicate that a DAGK type 3 (DAGKepsilon) which preferentially, but not selectively, utilizes 1-acyl-2-arachidonoyl-sn-glycerol and which could be associated with polyphosphoinositide resynthesis, participates in synaptic insulin signaling. GTP gamma S and NaF appear to be G protein activators related to insulin and the insulin receptor, both affecting the signaling mechanism that augments phosphatidic acid formation.

Analysis of oxygen binding by hemoglobin on the basis of mean intrinsic thermodynamic quantities.

The binding data for oxygenation of human hemoglobin, Hb, at various temperatures and in the absence and presence of 2,3-diphosphoglycerate, DPG, and inositol hexakis phosphate, IHP, were analyzed for extraction of mean intrinsic Gibbs free energy, DeltaGo, enthalpy, DeltaHo, and entropy, DeltaSo, of binding at various partial oxygen pressures. This method of analysis considers all the protein species present such as dimer and tetramer forms which were not considered by Imai et al. (Imai K et al., 1970, Biochim Biophys Acta 200: 189-196), in their analysis which was based on Adair equation. In this regard, the values of Hill equation parameters were estimated with high precision at all points of the binding curve and used for calculation of DeltaGo, DeltaHo and DeltaSo were also calculated by analysis of DeltaGo values at various temperatures using van't Hoff equation. The results represent the enthalpic nature of the cooperativity in Hb oxygenation and the compensation effect of intrinsic entropy. The interpretation of results also to be, into account the decrease of the binding affinity of sites for oxygen in the presence of DPG and IHP without any considerable changes in the site-site interaction (extent of cooperativity). In other words, the interactions between bound ligands, organic phosphates and oxygen, are more due to a decreasing binding affinity and not to the reduction of the cooperative interaction between sites. The results also document the more heterotropic effect of IHP compared to DPG.

Activation of the low oxygen affinity-inducing potential of the Asn108(beta)-->Lys mutation of Hb-Presbyterian on intramolecular alpha alpha-fumaryl cross-bridging.

The Asn108 beta-->Lys mutation in hemoglobin (HbPresbyterian mutation) endows a low O(2) affinity-inducing propensity to the protein. Introduction of a fumaryl cross-bridge between its two alpha 99 lysine residues also induces a low O(2) affinity into HbA. We have now engineered an alpha alpha-fumaryl cross-bridge into Hb-Presbyterian to determine the synergy or additivity, if any, that can be achieved between these two low O(2) affinity-inducing structural perturbations. Despite the presence of the additional epsilon-amino group of Lys108(beta) within the central cavity, the epsilon-amino group of Lys99(alpha alpha) of deoxy Hb-Presbyterian retained high selectivity for alpha alpha-fumaryl cross-bridging, with an overall efficiency comparable to that with HbA. The alpha alpha-fumaryl cross-linking of Hb-Presbyterian reduced its O(2) affinity much more significantly than that observed with HbA, indicating a synergy between the two low O(2) affinity-inducing structural perturbations. Apparently, the alpha alpha-fumaryl cross-bridge in Hb-Presbyterian activates part of the latent low O(2) affinity-inducing potential of Lys108(beta) that is generally activated in the presence of chloride. The synergy between the Asn108(beta)-->Lys mutation and the alpha alpha-fumaryl cross-bridging was conserved in the presence of chloride, but not in the presence of DPG. Furthermore, in the presence of chloride and DPG, alpha alpha-fumaryl Hb-Presbyterian accessed a low O(2) affinity T-state that is accessed by HbA, alpha alpha-HbA and Hb-Presbyterian only in the presence of IHP. Isoelectric focusing analysis suggested that the alpha alpha-fumaryl cross-linking of Hb-Presbyterian induces changes in the ionization behavior of one or more of the functional groups neighboring Lys99(alpha) and Lys108(beta) [presumably His103(alpha) and/or Glu101(beta)] to compensate for the extra positive charge of Lys108(beta). Molecular modeling studies identified two potential chloride binding sites per alpha beta dimer within the middle of the central cavity of alphaalpha-fumaryl HbA involving residues His103(alpha), Arg104(beta) and Asn108(beta). The affinity of these sites is increased in alpha alpha-fumaryl Hb-Presbyterian as a result of the Asn108(beta)-->Lys mutation. Thus, the results of the present study suggest that the enhanced neutralization of the positive charges in the middle of the central cavity of Hb achieved by these two electrostatic modifications, one (the alpha alpha-fumaryl cross-bridge) acting directly and the other (the Presbyterian mutation) acting indirectly through the mediation of chloride ion binding, facilitates the alpha alpha- fumaryl-Hb Presbyterian to access a low O(2) affinity T-state structure much more readily than either Hb-Presbyterian or alpha alpha-fumaryl HbA.

Oxygen Transport by Fetal Bovine Hemoglobin

The functional properties of fetal bovine hemoglobin have been studied as a function of temperature, chloride and 2,3-diphosphoglycerate (DPG) concentration. The fetal bovine erythrocyte has six times the concentration of the allosteric modulator DPG compared with the adult cell, and yet the oxygen affinity of the fetal hemoglobin still exceeds that of the adult molecule at the respective physiological concentration of DPG and at physiological temperature. We find that the allosteric modulator strongly affects the enthalpy of oxygen for the fetal hemoglobin but not for the adult protein. We propose that this may be an important mechanism for the exchange of heat from mother to fetus. In particular, under stripped conditions the oxygen affinity of fetal bovine Hb is considerably higher than that of the adult hemoglobin. Due to the higher DPG concentration that characterizes fetal bovine erythrocytes this difference is almost abolished in the presence of the respective physiological concentration of DPG and at 20°C. However, on going from 20°C to 37°C, the difference in O 2affinity between the two hemoglobins is restored, as it should if oxygen has to be transferred from maternal to fetal blood, by virtue of the lower overall heat of oxygenation (Δ H) displayed by fetal Hb when in the presence of DPG at physiological concentration. This behavior is reminiscent of that of human fetal Hb and outlines the role of temperature and of its interplay with heterotropic ligands in the modulation of hemoglobin function to fully meet the physiological needs of the organism.

Physiological Relevance of the Overall ΔH of Oxygen Binding to Fetal Human Hemoglobin

Human fetal hemoglobin is known to display, at 20°C, a lower affinity than human adult hemoglobin for oxygen when both proteins are in the absence of organic phosphates. The physiologically important reverse situation is achieved at 37°C upon addition of 2,3-bisphosphoglycerate (DPG), whose lower effect on fetal hemoglobin is related to some amino acid substitutions present in γ-chains. However, the difference in oxygen affinity observed at 37°C is not solely due to the different modulation power of DPG with respect to adult and fetal hemoglobins. In fact, the results presented here reveal new aspects linked to the interplay of temperature and organic phosphates.In particular, the lower effect of DPG on fetal hemoglobin renders almost identical the oxygen affinity of the two hemoglobins at 20°C, abolishing the difference observed in the absence of the effector. Successively on going from 20°C to 37°C, by virtue of the lower overall heat of oxygenation (ΔH) displayed by fetal hemoglobin when in the presence of DPG, adult hemoglobin shows a lower oxygen affinity, as it should if oxygen has to be transferred from maternal to fetal blood.

Development of antisickling compounds that chemically modify hemoglobin S specifically within the 2,3-diphosphoglycerate binding site

In this paper we describe a class of affinity reagents that react specifically with hemoglobin S at the 2,3-diphosphoglycerate binding site and effectively disrupt the sickling process. The prototype of these compounds is the bifunctional acylating agent bis(3,5-dibromosalicyl) fumarate. Previously it was shown that this compound reacts selectively with oxyhemoglobin to cross-link the β chains of the tetramer ( Walder et al., 1979 a ). The site of cross-linking has now been established by X-ray crystallographic studies to be from Lys82 β 1 to Lys82 β 2, spanning the DPG ‡ ‡ Abbreviations used: DPG, 2,3-diphosphoglycerate; p 50, partial pressure of oxygen needed to half-saturate hemoglobin; Hb, hemoglobin. binding site. The oxygen binding properties of the cross-linked hemoglobin are very similar to those of native hemoglobin A in the absence of DPG. However, in the presence of DPG, the oxygen affinity of the cross-linked hemoglobin is increased due to the blockade of the DPG site by the interchain bridge. This effect may indirectly interfere with the sickling process in vivo. More importantly the cross-link modification directly inhibits the polymerization of deoxyhemoglobin S. The solubility of the cross-linked derivative is increased by approximately 35% relative to that of native deoxyhemoglobin S. The X-ray crystallographic studies reveal that the cross-link strongly perturbs the acceptor site for Val6β in the lateral contact between molecules of deoxyhemoglobin S within the double strand of the sickle cell fiber. Our current hypothesis is that this structural perturbation weakens the lateral contact and is responsible for the observed increase in solubility. Due to the hydrophobic properties of the halogen substituents bis(3,5-dibromosalicyl) fumarate is able to traverse the red-cell membrane and, therefore, may be active in vivo. These studies provide the basis for further design and development of affinity reagents directed to the DPG binding site that may prove useful in the clinical management of sickle cell disease.

The interaction of some bis-arylhydroxysulphonic acids with a site of known structure in human haemoglobin.

1 Two bis-arylhydroxysulphonic acids were previously designed to interact with the known molecular configuration of the 2,3-diphosphoglycerate (DPG) receptor-site of human haemoglobin. These compounds liberate oxygen from the haemoglobin similarly to DPG. 2 Solutions of haemoglobin have now been observed under physiological conditions by nuclear magnetic resonance (n.m.r.) in the presence of DPG and of the compounds. 3 Two peaks in the n.m.r. spectrum of haemoglobin are shifted when DPG is added to the solution. 4 The same two peaks in the spectrum are affected by the compounds. 5 The observations are compatible with the predicted interaction between the compounds and the haemoglobin receptor site.

Thermodynamical studies of oxygen equilibrium of hemoglobin. Nonuniform heats and entropy changes for the individual oxygenation steps and enthalpy-entropy compensation.

Precise oxygen equilibrium curves of human adult hemoglobin were determined by the automatic recording method at several temperatures in the presence and absence of 2,3-diphosphoglycerate (DPG) or inositol hexaphosphate (IHP) with 0.05 M 2,2-bis(hydroxymethyl)-2,2',2''-nitrolotriethanol (bis-tris) buffers (pH 7.4) containing 0.1 M Cl-. The equilibrium data were analyzed according to the Adair scheme, and the heats, deltaHi (i = 1,2,3,4) and the entropy changes, deltaSi (i = 1,2,3,4), for the individual oxygenation steps were obtained. The shape of the equilibrium curve varies on temperature changes whether DPG or IHP is present or absent. In consequence, the deltaHi value depends on i and on the presence of DPG and IHP. Behavior of deltaSi is similar to that of deltaHi. The similar behavior of deltaHi and deltaSi resulted in a compensation phenomenon. The contribution of T cdeltaSi to the free energy change is compensated by the contribution of deltaHi at the first three oxygenation steps but not at the fourth step, and for i = 1,2, and 3 changes of T cdeltaSi value upon the addition of DPG and IHP are compensated by accompanied changes of deltaHi value, where T c (= 260 K) is the compensation temperature. A major part of both the enthalpy-entropy compensation and nonuniformity of deltaHi and deltaSi appears to be attributable to contributions of the oxygen-linked binding of Cl-, DPG and IHP, by hemoglobin. The present results do not necessarily support the earlier idea of Wyman that the cooperative oxygenbinding is essentially an entropy effect.

The interaction of 2,3-diphosphoglycerate on human deoxy and oxyhemoglobin

A very accurate pH stat method was used to measure the number of protons which are taken up when 2,3-diphosphoglycerate (DPG) reacts with deoxyhemoglobin (Hb) and oxyhemoglobin (HbO2). As judged by this method it appeared that the effect of DPG on both Hb and HbO2 is pH dependent with this difference that similar results are obtained at different pH ranges. The data showed that the additional Bohr effect and therefore the oxygen affinity of hemoglobin in the presence of DPG is not only due to the binding of DPG to Hb, but also due to the interaction of DPG with HbO2.

Vulcanization of Elastomers. 26. Vulcanization of Natural and Synthetic Rubbers by Sulfur in the Presence of Organic Bases

Abstract In connection with earlier research work, we have carefully studied the decrease of sulfur during the vulcanization of Perbunan N 2818 in the presence of DPG, at various temperatures and with varied molar concentrations of sulfur and accelerator. We found : 1. The sulfur concentration decreases at all temperatures according to a time law of order 0.8. An activation energy of about 28 kcal/mole is derived from the temperature dependence of the rate constant. 2. The reaction order is independent of the initial concentration of reactants. 3. A discrepancy is found in the order of the reaction with respect to time and with respect to concentration, and it is clearly shown that the dependence of the initial rate on the initial concentration can not be expressed by a single power law. 4. The attempt is made to explain the discrepancy by postulating catalysis by an intermediate compound. The consequences from this consideration are compared with the experimental results, and, on the whole, agreement is found between theory and experiment.