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Query: UNIPROT:Q0Z944 (hemoglobin)
 63,986 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To determine the effect of changing concentrations of uremic metabolites on factors affecting oxygen transport, without the effects of extracorporeal blood pumping, we studied five patients before, during and after peritoneal dialysis. Significant decreases in serum urea, creatinine and phosphate and increase in serum bicarbonate were not associated with changes in P50, a reflection of hemoglobin-oxygen affinity. High erythrocyte 2,3-DPG concentrations decreased only slightly. Arterial pO2 increased slightly as negative fluid balance was achieved. The slight changes in oxygen transport parameters with dialysis suggest an interplay of compensatory factors and do not warrant modifying dialysis to limit the correction on acidosis or hyperphosphatemia. Effects on hemoglobin and pO2 resulting from fluid loss can be the dominant influence of peritoneal dialysis on tissue oxygenation.
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PMID:Influence of peritoneal dialysis on factors affecting oxygen transport. 0 Jun 31

1. An activator of the (Ca2+ plus Mg2+)-stimulated ATPase present in the human erythrocytes (membrane) has been isolated in soluble form from hemolysates of these cells. Partial purification has been achieved through use of carboxymethyl-Sephadex chromatography. The resulting activator fraction contained no hemoglobin and only 0.3% of the total adenylate kinase activity of the cell. 2. Whereas the activator was released from erythrocytes subjected to hemolysis in 20 miosM buffer at pH 7.6 or at pH 5.8, only the membranes prepared at pH 7.6 were affected by it. 2. Whereas the activator was released from erythrocytes subjected to hemolysis in 20 miosM buffer at pH 7.6 or at pH 5.8, only the membranes prepared at pH 7.6 were affected by it. 3. When (Ca2+ plus Mg2+)-ATPase activity was measured by 32Pi release from (gamma-32P)ATP, freeze-thawed erythrocytes, as well as membranes prepared at pH 5.8 and at pH 7.6, expressed lower values than noted by assay for total Pi release. When ADP instead of ATP was used as substrate, significant amount of Pi were released by these erythrocyte preparations. Further study revealed (a) production of ATP and AMP from ADP with membranes and hemolysate alone, and (b) exchange of the gamma-and B-position phosphate on (gama-32P)ATP in the presence of membranes plus hemolysates. These observations established the presence of adenylate kinase activity in the (membrane-free) hemolysates and in membranes. It further supports the conclusion that Pi release from ADP by human erythrocytes (freeze-thawed) and by their isolated membranes is due to formation of ATP by adenylate kinase and hydrolysis of this generated ATP by (Ca2+ plus Mg2+)-ATPase. 4. The following points were also established: (a) absence of an ADPase in human erythrocytes; (b) the (Ca2+ plus Mg2+)-ATPase activator enhanced cleavage only of the gama-position of ATP and (c) the (Ca2+ plus Mg2+)-ATPase activator is neither adenylate kinase nor hemoglobin.
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PMID:Studies on an activator of the (Ca2+ plus Mg2+)-ATPase of human erythrocyte membranes. 0 Oct 98

Comparative data on quaternary structure, cooperativity, Bohr effect and regulation by organic phosphates are reviewed for vertebrate hemoglobins. A phylogeny of hemoglobin function in the vertebrates is deduced. It is proposed that from the monomeric hemoglobin of the common ancestor of vertebrates, a deoxy dimer, as seen in the lamprey, could have originated with a single amino acid substitution. The deoxy dimer has a Bohr effect, cooperativity and a reduced oxygen affinity compared to the monomer. One, or two, additional amino acid substitutions could have resulted in the origin of a tetrameric deoxy hemoglobin which dissociated to dimers on oxygenation. Gene duplication, giving incipient alpha and beta genes, probably preceded the origin of a tetrameric oxyhemoglobin. The origin of an organic phosphate binding site on the tetrameric hemoglobin of an early fish required only one, or two, amino acid substitutions. ATP was the first organic phosphate regulator of hemoglobin function. The binding of ATP by hemoglobin may have caused the original elevation in the concentration of ATP in the red blood cells by relieving end product inhibition of ATP synthesis. The switch from regulation of hemoglobin function by ATP to regulation by DPG may have been a consequence of the curtailment of oxidative phosphorylation in the red blood cell. The basic mechanisms by which ATP and DPG concentrations can respond to strss on the oxygen transport system were present before the origin of an organic phosphate binding site on hemoglobin. A switch from ATP regulation to IP5 regulation occurred in the common ancestor of birds.
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PMID:Hemoglobin function in the vertebrates: an evolutionary model. 0 43

1. The chemical shifts (delta) of the phosphates of 2,3-diphosphoglycerate and adenosine triphosphate (ATP) were determined by phosphorus nuclear magnetic resonance (31P NMR) spectroscopy and were found to be displaced downfield following the addition of hemoglobin (3 mM) to a solution of either diphosphoglycerate (5 mM) or ATP (1 mM). 2. The binding of these compounds to hemoglobin was also determined by membrane ultrafiltration. A direct relationship was observed between the change in chemical shift ((delta delta) of the 2-P and 3-P of diphosphoglycerate and the percent diphosphoglycerate bound, when the latter was varied by altering pH, oxygenation state, or total diphosphoglycerate concentration. 3. In comparable studies with ATP binding, a linear relationship between the delta delta values of the gamma-, beta-, and alpha-P of ATP and the percent of ATP bound was not observed when the data from all of the experiments were plotted. NMR signals were not detectible in deoxyhemoglobin solutions containing 1 mM ATP but were seen in solutions containing 3.8 mM ATP. 4. The results indicate that 31P NMR spectroscopy is a promising tool for investigating organic phosphate interactions with hemoglobin.
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PMID:Interactions between hemoglobin and organic phosphates investigated with 31P nuclear magnetic resonance spectroscopy and ultrafiltration. 0 26

An automated AutoAnalyzer method using 5:5'-dithiobis-2-nitrobenzoic acid is described for determining whole blood glutathione reductase (BGR) activity and for measuring in vitro activation of BGR with flavin adenine dinucleotide (FAD). BGR activity is expressed as mumoles glutathione regenerated from oxidized glutathione per ml of whole blood (WB) or per g of hemoglobin. The stimulatory effect of FAD on BGR activity divided by the activity without FAD determined the activity coefficient (AC). We found that NADPH and oxidized glutathione assay concentrations of 0.100 mmole/liter and 0.250 mmole/liter, respectively, in 0.1 mole/liter phosphate buffer, pH 7.4, gave consistent results when WB, before assay, was diluted 20-fold. WB samples to be stored are initially diluted 10-fold with distilled water and frozen. Prior to assay, two aliquots of the sample are diluted 2-fold, one aliquot with distilled water and another with 46 mumole/liter FAD. With sample and manifold dilutions the assay FAD concentrations is 1.0 mumole/liter: assay concentrations greater than 5.0 mumole FAD/liter were shown to be inhibitory. We examined blood samples from 617 children in the age range 6 to 60 months and determined the normal AC range to be between 1.00 and 1.35. Six weaned rats (23 days of age), maintained on a riboflavin-deficient diet, showed a mean AC of 1.23, 1.54, 2.02, and 2.41 at 23, 26, 30, and 36 days of age, respectively. Six control rats maintained an AC of 1.23 +/- 0.05 (SD) during the same period.
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PMID:An automated flavin adenine dinucleotide-dependent glutathione reductase assay for assessing riboflavin nutriture. 0 81

The temperature dependence of the oxygen equilibrium of tadpole hemoglobin has been determined between 0 degrees and 32 degrees for the unfractionated but phosphate-free lysate and between 12 degrees and 32 degrees for each of the four isolated components between pH 6 and 10 in 0.05 M cacodylate, Tris, or glycine buffers containing 0.1 M NaCl and 1 mM EDTA. Under these conditions the Bohr effect (defined as deltalog p50/deltapH) of the unfractionated lysate is positive at low temperatures between pH 6 and 8.5 and is negative above pH 8.5 to 8.8 at any temperature. As the temperature rises the Bohr effect below pH 8.5 changes greatly. In the interval pH 7.0 to 7.5, the magnitude of the Bohr effect decreases from + 0.28 at 0 degrees to zero at about 24 degrees and becomes negative, as in mammalian hemoglobins, above this temperature. Measurements with the isolated components show that the temperature dependence of oxygen binding for Components I and II and for Components III and IV is very similar. For both sets of components the apparent overall enthalpy of oxygenation at pH 7.5 is about -16.4 kcal/mol and -12.6 kcal/mol at pH 9.5. The measured enthalpies include contributions from the active Bohr groups, the buffer ions themselves, the hemoglobin groups contributing buffering, and any pH-dependent, oxygenation-dependent binding of ions such as chloride by the hemoglobin. The apportioning of the total enthalpy among these various processes remains to be determined. Between pH 8 and 10.5 tadpole oxyhemoglobin undergoes a pH-dependent dissociation from tetramer to dimer. The pH dependence of the apparent tetramer-dimer dissociation constant indicates that at pH 9.5 the dissociation of each tetramer is accompanied by the release of approximately 2 protons. In this pH range the oxygen equilibrium measurements indicate that about 0.5 proton is released for each oxygen molecule bound. The results are consistent with the conclusion that one acid group per alphabeta dimer changes its pK from about 10 to 8 or below upon dissociation of the tetramer.
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PMID:Hemoglobins of the tadpole of the bullfrog, Rana catesbeiana. Temperature dependence of oxygen binding and pH dependence of subunit dissociation. 0 73

The interaction of organic phosphates with hemoglobin is studied by use of a simple thermodynamic approach. A model-independent analysis is employed to evaluate the accuracy of Adair constants determined in the presence of 2,3-diphosphoglycerate (DPG). The change of oxygen affinity in the presence of phosphates is related to the macroscopic phosphate binding constants of oxy- and deoxyhemoglobin and used to extract such binding constants from oxygen equilibrium measurements. The change of the Bohr effect in the presence of phosphates and the competitive binding of carbon dioxide and DPG are treated quantitatively. The binding of organic phosphates is incorporated into an allosteric model, in which the effect of phosphate on both tertiary and quaternary structure changes is included. By use of this model, the factors which can be responsible for the increased functional heterogeneity of alpha and beta chains in the presence of phosphates are clarified.
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PMID:Analysis of the interaction of organic phosphates with hemoglobin. 0 91

The Bohr effect of hemoglobin and that of the aquomet and cyanomet valency hybrids was measured in the presence and the absence of IHP (inositol hexaphosphate) and DPG (2,3-diphosphoglycerate). In the absence of these organic phosphates the four hybrids show similar, but suppressed Bohr effects as compared to hemoglobin. Addition of IHP and DPG results in all cases in an increase of the Bohr effect. The additional phosphate induced Bohr effect of the hybrids with the alpha chain in the oxidized form is almost identical to that of hemoglobin, while this effect of the hybrids with oxidized beta chains is slighly lower than that of hemoglobin. The results suggest (a) that the Bohr effect is correlated to the ligation state of the hemoglobin molecule rather than to its quaternary structure (b) that the additional phosphate induced Bohr effect is related to the change in quaternary structure of the tetramer, and (c) that with respect to the Bohr effect of the hybrids there is no difference between high and low spin species.
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PMID:The influence of organic phosphates on the Bohr effect of human hemoglobin valency hybrids. 0 27

Oxyhemoglobin dissociation curves (ODC) from zero to full saturation were developed from tests performed on whole blood from various groups of diabetic and nondiabetic healthy subjects. P50 at in-vivo pH was slightly but significantly lower than normal in ambulatory nonacidotic, uncomplicated juvenile diabetics (26.0 vs. 27.3 mm. Hg, P less than 0.001), despite increased red cell 2,3-diphosphoglycerate (2,3-DPG) concentrations in diabetic erythrocytes (15.0 vs. 13.7 mumole/gm. Hb, P less than 0.001). This combination of changes is in keeping with the presence of increased proportions of hemoglobin AIc in insulin-treated diabetics. The position of the ODC was positively correlated with the 2,3-DPG concentration (P less than 0.01), which varied in response to fluctuations in plasma concentration of inorganic phosphate (Pi) (P less than 0.001). Optimal metabolic control may lead to a normalization of the ODC in association with increased concentrations of red cell 2,3-DPG and P. When the diabetes was uncontrolled, the ODC was usually unchanged during the acidotic phase because the lowered pH balanced the effect of diminished 2,3-DPG concentration on the ODC. After correction of acidosis, the disproportion between erythrocyte 2,3-DPG and pH became quite prominent, accompanied by a corresponding fall in P50 (21.0 vs. 26.1 mm. Hg, P less than 0.001). Following ketoacidosis, with a persistently lowered Pi, it may take up to one week for 2,3-DPG to return to an approximately normal level, and the P50 will be impaired for the same period. A diphosphonate (EHDP) known to enhance tubular phosphate reabsorption in man was given to nonacidotic insulin-treated diabetic and healthy volunteers for 28 days. It caused a significant increase in mean Pi and P50 in both healthy and diabetic subjects (r = 0.58, P less than 0.01). When a dietary supplement of dibasic calcium phosphate was given to diabetic subjects for 28 days, a significant increase in P50 also occurred (25.2 vs. 27.2 mm. Hg, P less than 0.001). It is recommended that the diabetes diet be supplemented by dibasic calcium phosphate to prevent the inhibitory effect of a low concentration of Pi on red cell oxygen delivery.
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PMID:Oxygen transport impairment in diabetes. 0 22

The pH dependence of the apparent tetramer to dimer dissociation constant has been determined at 20 degrees for both oxy- and deoxyhemoglobins A and Kansas. These measurements were made by three different procedures: gel chromatography, sedimentation velocity, and kinetic methods in either of three buffer systems: 0.05 M cacodylate, Tris, or glycine with 1 mM EDTA and 0.1 M NaCl between pH 6.5 and 11. The tetramer-dimer dissociation constant of human oxyhemoglobin A decreases from about 3.2 X 10(-6) M at pH 6.0 to about 3.2 X 10(-8) M at pH 8.5. The slope of this line indicates that the dissociation of tetramer to dimer is accompanied by the uptake of about 0.6 protons per mol of tetramer in this region. The corresponding dissociation constant for deoxyhemoglobin in the same pH region increases apparently almost linearly from 1.0 x 10(-12) M at pH 6.5 to about 1.0 x 10(-5) M at pH 11. To dimer is associated with the release of about 1.6 protons per mol of tetramer. Comparison of these data with the known proton release accompanying the oxygenation of tetramers confirms that the pH dependence of oxygen binding by dimers must be very small. The present data predict that the overall proton release or uptake per oxygen bound by dimer should be less than 0.1. The tetramer-dimer dissociation equilibria of oxy- and deoxyhemoglobins above pH 8.5 have identical pH dependences. In this range the dissociation constant of deoxy-Hb is about one-tenth that of oxyhemoglobin. Human oxyhemoglobin Kansas is known to have an enhanced tetramer-dimer dissociation compared with that of hemoglobin A. Below pH 8.5 the tetramer-dimer dissociation constant of Hb Kansas is about 400 times greater than that of HbA in the absence of phosphate buffers. In contrast, the tetramer-dimer dissociation constants of deoxyhemoglobins A and Kansas appear to be identical. These findings are consistent with previous structural observations on these hemoglobins. The data on the tetramer-dimer dissociation of human hemoglobin were used to calculate the total free energy of binding of oxygen to the tetramer and the median oxygen pressure on the basis of fundamental linkage relations and a pH-independent estimate of the total free energy of binding oxygen to dimer. Simulated oxygen binding curves were generated with the equations of Ackers and Halvorson (Ackers, G. K., and Halvorson, H. (1974) Proc. Natl. Acad. Sci. U.S.A. 71, 4312-4316) by making two assumptions: (a) that the dimers are noncooperative and pH-independent in O2 binding and (b) that the distribution of cooperative energy in the oxygenation of tetramers is independent of pH. We have compared these simulations with experimental data obtained at low protein concentrations (30 to 124 muM heme) to show that the variation in oxygen affinity with pH can be described in terms of the subunit equilibria. We conclude that an accurate analysis of the contributions of individual oxygen binding steps to the Bohr effect cannot be made without considering the contributions of the dimers to oxygen binding...
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PMID:Tetramer-dimer dissociation in homoglobin and the Bohr effect. 0 90


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