Effect 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.

Regulation of blood oxygen transport in hibernating mammals.

Along with the periodic reductions in O2 requirements of mammalian hibernators during winter, the O2 affinity of the blood of mammalian hibernators is seasonally regulated to help match O2 supply to consumption, contributing to limit tissue oxidative stress, particularly at arousals. Specifically, mammalian hibernators consistently show an overall increase in the blood-O2 affinity, which causes a decreased O2 unloading to tissues, while having similar or lower tissue O2 tensions during hibernation. This overview explores how the decreased body temperature and concentration of red blood cell 2,3-diphosphoglycerate (DPG) that occur in hibernation contribute separately or in combination to the concurrent increase in the O2 affinity of the hemoglobin, the O2 carrier protein of the blood. Most mammalian hemoglobins are responsive to changes in DPG concentrations, including that of the hibernating brown bear, although the smaller hibernators, such as golden-mantled ground squirrel, chipmunks, and dormice, have hemoglobins with low sensitivity to DPG. While the effect of DPG on oxygenation may vary, the decrease in body temperature invariably increases hemoglobin's O2 affinity in all hibernating species. However, the temperature sensitivity of hemoglobin oxygenation is low in hibernators compared to human, apparently due in part to endothermic allosteric quaternary transition in ground squirrels and dissociation of chloride ions in brown bears. A low heat of blood oxygenation in temporal heterotherms, like hibernators, may thus contribute to reduce heat loss, as found in regional heterotherms, like polar mammals, although the significance would be low in winter hibernation.

Influence of Allosteric Effectors and Temperature on Oxygen Binding Properties and the Bohr Effect of Bovine Hemoglobin

The O2 binding properties of bovine Hb were examined. The increase in Cl- and DPG concentration enhanced P50. A reduction in n(max) was observed at high Cl- concentration, while DPG had little effect on n(max). An increase in Cl- concentration enhanced the Bohr effect, the magnitude of which reached a maximum at 0.1 M Cl- and 20 degrees C. This concentration is nearly equal to that at the highest slope of the log P50 vs. log [Cl-] plot, and also equal to the physiological Cl- concentration (0.1 M) of bovine blood. Furthermore, the influence of Cl- concentration on the Bohr effect is independent of temperature. On the other hand, in the absence of Cl-, bovine Hb is sensitive to DPG; an increase in DPG concentration enhanced the Bohr effect, which reached a maximum at 3 mM DPG and 20 degrees C. This concentration is nearly equal to that at the highest slope of the log P50 vs. log [DPG] plot. At low DPG concentrations, the DPG effect on the Bohr effect became small with increasing temperature, whereas at high DPG concentrations, the DPG effect was insensitive to temperature changes. At the physiological concentration of DPG (0.5 mM), increases in both Cl- concentration and temperature diminished the DPG effect. At the physiological concentrations of Cl- and DPG, the Bohr effect was -0.36 at 37 degrees C. The deltaH value at the physiological concentrations of Cl- and DPG was approximately -5.8 kcal/mol at pH 7.4. These results indicate that Cl- and temperature are important determinants of the O2 binding properties of bovine Hb.

Hemoglobin, pH and DPG/chloride shifting

In this study a decreased DPG response by polar bear ( Ursus maritimus) hemoglobin was observed, and this response was interpreted as an example of gradual DPG/chloride shifting. This sort of mechanism has been suggested to occur in ruminants and, intuitively, one might guess that for ruminants the DPG/Cl – shifting might have been beneficial and hence selected for at the time of the latest Ice Âge. However, suggestion that this is purely a temperature effect in polar bears and ruminants conflicts with the existence, in the hot savanna, of mammals that have Hb modulated by chloride. However, acidosis effects caused by routine periods of food shortage, induced in extreme environments may explain the responses of the hemoglobins of animals adapted to extreme habitats. The chloride effect is bound to specific amino acid substitutions in key positions. In polar bear Hb, they are specific, additional (with respect to human HbA) O 2-linked chloride binding sites located between Lys-76 (β) and Lys-8 (β). The amino acids operate as an additional H + binding site for a chloride anion. Additionally, with respect to human adult HbA, the primary structure of polar bear Hb was characterized by two substitutions in β chains: Pro-5 (A2)→ Gly and Ala-76 (E20)→Lys. The increased flexibility of the A helix causes the lower DPG effect. We further hypothesize that the resulting widening of the central cavity allows the Lys-82 (β) terminus to be free and constitute an additional, chloride-binding site.

Regulation of linkages between the erythrocyte membrane and its skeleton by 2,3-diphosphoglycerate

In addition to reducing hemoglobin-O2 affinity, 2,3-diphosphoglycerate (DPG) is known to modulate the mechanical properties of the erythrocyte membrane. By fluorescence spectroscopy and differential scanning calorimetry, we demonstrate that DPG binds the cytoplasmic domain of erythrocyte membrane band 3 in two stages characterized by apparent KD values of approximately approximately 2 and 12 mM. DPG was also shown to perturb the stability of ankyrin, protein 4.1, and protein 4.2 in situ and to directly bind to protein 4.1. In studies of membrane-skeleton interactions, DPG was observed to inhibit the fast and slow phases of ankyrin binding to band 3 and to reduce both the number of ankyrin sites and affinity of ankyrin for each class of site. The inhibition was biphasic, similar to the band 3-DPG binding isotherm; however, at physiological DPG concentrations a reduction in only 15% of the ankyrin sites was observed. In contrast, inhibition of protein 4.1 binding to the membrane reached 65% at physiological DPG concentrations (approximately approximately 5.9 mM); at more elevated concentrations, blockade was nearly quantitative, affecting glycophorin and band 3 sites alike. Taken together with previous observations, these data suggest that DPG's effect on O2 delivery may extend beyond its well recognized impact on hemoglobin-O2 affinity.

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.

The effect of 2,3-diphosphoglycerate on the solubility of deoxyhemoglobin S

Although highly charged polyanions, such as inositol hexaphosphate, have been clearly shown to decrease the solubility of deoxyhemoglobin S, the effect of 2,3-diphosphoglycerate (DPG), the endogenous allosteric effector within the red cell, has been more controversial. In this work we have compared the effect of DPG on the solubility of native deoxyhemoglobin S and a derivative in which the DPG binding site is blocked by crosslinking the two β82 lysine residues. At pH 6.6 and 30 °C the solubility of deoxyhemoglobin S was found to be decreased by 15% (i.e., from 18.8 to 16.0 g/dl) in the presence of saturating concentrations of DPG. Under the same conditions DPG had no effect on the solubility of the cross-linked derivative. This result establishes unequivocally that the binding of DPG within the β cleft directly facilitates the polymerization of deoxyhemoglobin S. Under physiological conditions, the solubility of deoxyhemoglobin S was found to be decreased by 6% in the presence of an equimolar concentration of DPG. A solubility decrease of this magnitude is sufficient to enhance the tendency of SS cells to sickle and may exacerbate the clinical symptoms of sickle cell disease.

Studies of haemoglobin functions by site-directed mutagenesis

Human (3-globin was synthesized in Escherichia coli as a cleavable fusion protein by using the expression vector pLcIIFX|3-globin(nic - ). The authentic (3-globin was liberated by digestion with blood coagulation factor X a and a 2 (3 2 tetramers were reconstituted. The oxygen-binding properties of reconstituted haemoglobin (Hb) were essentially the same as those of human native Hb. Two mutant haemoglobins were constructed by site-directed mutagenesis. HbNymphéas (Cys-93(3->Ser) showed a slightly increased oxygen affinity and diminished co-operativity with normal DPG (2,3-diphosphoglycerate) effect and slightly reduced alkaline Bohr effects. Hb Daphne (Cys-93(3->-Ser, His-143(3->- Arg) showed low co-operativity with high oxygen affinity. The alkaline Bohr effect was slightly reduced, but the DPG effect was enhanced by 50% by the His-143(3^ Arg mutation.

Deoxygenated sickle hemoglobin. Modulation of its solubility by 2,3-diphosphoglycerate and other allosteric polyanions.

The effects of 2,3-diphosphoglycerate (DPG) and other allosteric polyanions of the phosphate or sulfate ester class (inositol hexaphosphate (IHP), ATP, pyridoxamine-5'-phosphate (PMP), and inositol hexasulfate (IHS] on the solubility of deoxyhemoglobin S, and the oxygen affinity of Hb A were evaluated. Their effects on the saturation concentration (csat) indicated promotion of gelation in each case, according to the following order of molar effectiveness: IHP greater than IHS greater than DPG greater than ATP much greater than PMP. Four polybasic carboxylic acids (benzenetricarboxylate (trimesic acid), benzenetetracarboxylate (BTC), benzenepentacarboxylate (BPC), and benzenehexacarboxylate (BHC] were evaluated as well. Their order of molar effectiveness was: BHC greater than BPC greater than BTC much greater than trimesic acid. Both classes of polyanions influenced oxygen affinity in the same order as solubility. Overall, a good correlation existed between the negative charges of these nine allosteric polyanions at neutral pH and their effects on solubility and oxygen affinity. Because of its possible role in the pathophysiology of sickle cell disease, the effect of DPG on csat was examined over the pH range 6.5-7.6. While a decrease in csat was observed for DPG-saturated deoxyhemoglobin S throughout this range, the decrement observed in the physiological pH range (1.8 g/dl) was somewhat lower than that below neutral pH (3.0 g/dl); in either case the sickling tendency of SS red cells would be enhanced. Inasmuch as the intracellular concentration of DPG in sickle cell anemia may be elevated as much as 2-fold, maneuvers aimed at its reduction could be therapeutically beneficial.

Oxygen equilibrium of larval and adult hemoglobins of the salamander, Pleurodeles walt II

1. 1. Larval red blood cells exhibited a higher oxygen affinity and a lower cooperativity than adult red blood cells. 2. 2. The Bohr effect was found equal to zero for the larval red blood cells. 3. 3. The two main fractions Hb A and Hb B found in adult red blood cells have different oxygen affinities and DPG effect, but the same normal cooperativity, and the same Bohr effect, slightly positive and “reverse” in comparison to that of mammalian hemoglobins.

Modification of hemoglobin S with dimethyl adipimidate contribution of inter-tetrameric cross-linking to changes in properties

Treatment of purified hemoglobin S with dimethyladipimidate (DMA), which results in inter- as well as intra-tetrameric cross-linking, induces an increase in oxygen affinity, a decrease in 2,3-diphosphoglyceric acid (DPG) effect and an increase in solubility of deoxyhemoglobin S. To determine the contribution of inter-tetrameric cross-linking to these changes, we isolated cross-linked components from DMA-modified hemoglobin S and from hybrids containing either a or β s -treated subunits ( α t β c s or α c β t s ) and determined their oxygen affinity, interaction with DPG, solubility and kinetics of aggregation. Intermolecular cross-linking occurred only through β s subunits, while intra-tetrameric cross-links involved both α and β s subunits. Cross-linked hemoglobin tetramers exhibited higher oxygen affinity, lower cooperativity and decreased DPG effect compared to non-cross-linked tetramers. The solubility of DMA-modified deoxyhemoglobin S decreased from 27.1 g/dl to 22.0 g/dl following removal of inter-tetramerically cross-linked derivatives. The delay time, usually observed prior to aggregation of dilute deoxyhemoglobin S in 1.8 M phosphate, was abolished by DMA modification, but restored following removal of cross-linked hemoglobin tetramers. Cross-linked hemoglobin S tetramers isolated from DMA-treated hemoglobin S did not aggregate when deoxygenated. In contrast to the results in dilute solution, concentrated solutions of DMA-treated deoxyHb-S exhibited prolonged delay times prior to polymerization. These results demonstrate that inter-tetrameric cross-linking contributes to the antisickling properties of DMA by increasing oxygen affinity, increasing solubility and disrupting the aggregation of hemoglobin S.

Studies on diphenylguanidine–accelerated sulfur vulcanization of styrene butadiene rubber in the presence and absence of dicumylperoxide

AbstractDiphenylguanidine (DPG) raises the rate of decomposition of dicumylperoxide (DCP) and the crosslinking maxima due to DCP is lowered to some extent by DPG. When the molar proportion of DPG–S is approximately 1:1, no additive results of crosslink formation (as reported for NR) are observed. Zinc oxide and stearic acid increase the rate of crosslinking as well as the crosslinking maxima. In the present study it appears most probable that DPG‐accelerated sulfuration of SBR is an ionic process. At a constant level of DCP and sulfur crosslink density increases when the amount of DPG is increased; a constant level of DCP and DPG crosslinking increases with rising sulfur concentration.An increase in the concentration of DPG or sulfur leads to greater formation of the complex as well as a change in its composition. The effect of DPG is more pronounced, for by reducing the number of sulfur atoms more sulfur is available for crosslinking. Sulfur absorbs little SO2 or H2S; if it is already saturated, there is no perceptible effect. DPG does absorb H2S or SO2 and the rate and maxima of crosslinks is increased. The effect of SO2 is higher because of the higher Ka values of H2SO3 and consequently higher concentration of HSO3−. Reversion is a free‐radical process inhibited by free DPG present in the system. In the presence of zinc oxide and stearic acid the reaction follows a polar mechanism as well as a radical mechanism.

The theoretical effect of DPG upon oxygen diffusion in erythrocytes.

The physiological significance of intra-erythrocyte haemoglobin (Hb)-facilitated oxygen transport (HFOT) has been debated since the observation (Wittenberg 1959; Scholander 1960) that steady-state O2 transfer across a thin layer of solution is accelerated by this heme-bearing protein. An authoritative review has been published by Kreuzer (1970).

Influence of temperature on hemoglobin-ligand interaction in whole blood.

Temperature-dependent change in hemoglobin-oxygen affinity was measured as a function of hemoglobin-oxygen saturation. In addition, the CO2 Bohr factor and fixed acid Bohr factor were measured as a function of saturation of temperatures of 23, 30, 37, and 44 degrees C. Measurements were made on normal blood and blood with reduced 2,3-diphosphoglycerate (DPG). The influence of temperature is greatest at low saturation and is enhanced slightly by DPG depletion. The CO2 Bohr factor is increased at high temperatures; this is primarily due to increased carbamino formation with rising temperature, especially at lower oxygen saturation. The effect of DPG on oxygen affinity is reduced at a high temperature and elevated at low temperature. These diverse effects of temperature on hemoglobin-ligand interaction require consideration in assessing oxygen delivery when temperature is increased or decreased.

Differential effects of 2,3-DPG, ATP and inositol pentaphosphate (IP5) on the oxygen equilibria of duck embryonic, fetal and adult hemoglobins

1. 1. In addition to the fetal and adult hemoglobins (F, A and D) already described in the Peking Duck, there are two embryonic hemoglobins (E 1 and E 2) which disappear by day 21 of incubation. 2. 2. Fetal hemoglobin does not exhibit any specific 2,3 DPG effect, in spite of the fact that this is the major red cell phosphorylated intermediate during the last quarter of the prehatching period. Conversely, embryonic hemoglobins are sensitive to IP5 in spite of the fact this compound is absent in the corresponding red cells. 3. 3. ATP preferentially lowers the oxygen affinity of Hb A. 4. 4. IP5 is the major organic phosphate effector with respect to oxygen affinity in vitro in all duck hemoglobins studied. 5. 5. Hb D exhibits an increased Bohr effect as compared with Hbs A and F. 6. 6. Considering the organic phosphates present at each period of development, the corresponding hemoglobin pattern, and the p50 induced by these phosphorylated compounds we suggest that there is a need for a higher oxygen affinity for the red cells during the immediate pre-hatching period and that 2,3 DPG could be the appropriate phosphate modulator for this phenomena.

Abnormal functional properties of Hb hope αC A2β 2 (H14) Gly → Asp: A low oxygen affinity hemoglobin with decreased DPG effect

Abnormal functional properties of Hb hope αC A2β 2 (H14) Gly → Asp: A low oxygen affinity hemoglobin with decreased DPG effect

Hemoglobin Little Rock (β143 (H21) His→Gln): EFFECTS OF AN AMINO ACID SUBSTITUTION AT THE 2,3-DIPHOSPHOGLYCERATE BINDING SITE

Abstract The amino acid substitution of hemoglobin Little Rock (HbLR) is here defined as β143 (H21) His → Gln, a site which is important for binding of 2,3-diphosphoglycerate (HbA). Studies of the effect of DPG and of chloride and phosphate on the oxygen affinities of chromatographically isolated HbLR and HbA show that HbLR has a much higher oxygen affinity than HbA at all anion concentrations. The shapes of the titration curves are consistent with binding of each species of anion studied to both the deoxy and oxy conformations of hemoglobin. Equations were developed from simple equilibrium models to calculate anion dissociation constants from the oxygen equilibrium data. The model for DPG binding assumed one oxygen-linked binding site per hemoglobin tetramer, and that for small anion binding assumed two sites. The DPG dissociation constant for deoxy HbLR (Kd = 3.3 x 10-5 m) is approximately twice that of deoxy HbA (Kd = 1.8 x 10-5 m), while the dissociation constant for oxy HbLR (Ko = 7.0 x 10-3 m) is four times that of oxy HbA (Ko = 1.7 x 10-3 m). Dissociation constants for chloride (HbLR: Kd = 2 x 10-3 m, Ko = 0.6 m; HbA: Kd = 2 x 10-3 m, Ko = 0.4 m) and phosphate (HbLR: Kd = 3 x 10-4 m, Ko = 0.1 m; HbA: Kd = 2.5 x 10-4 m, Ko = 0.1 m) are larger than the corresponding constants for DPG for both hemoglobins. However, the differences between HbLR and HbA in the binding of these anions are not significant. These data indicate the importance of the β143 histidine for the binding of DPG, but not of small anions, to HbA in solution. These findings appear to be in good agreement with crystallographic observations reported by Arnone ((1972) Nature 237, 146–149).

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.

Effect of 2,3-diphosphoglycerate and H+ on the raction of O 2 and hemoglobin.

ARTICLESEffect of 2,3-diphosphoglycerate and H+ on the raction of O 2 and hemoglobinC Bauer, RA Klocke, D Kamp, and RE ForsterC Bauer, RA Klocke, D Kamp, and RE ForsterPublished Online:01 Apr 1973https://doi.org/10.1152/ajplegacy.1973.224.4.838MoreSectionsPDF (3 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByO2 permeability of lipid bilayers is low, but increases with membrane cholesterol25 October 2021 | Cellular and Molecular Life Sciences, Vol. 78, No. 23The rate of the deoxygenation reaction limits myoglobin- and hemoglobin-facilitated O2 diffusion in cellsVolker Endeward1 May 2012 | Journal of Applied Physiology, Vol. 112, No. 9Erratum to: Blood HbO2 and HbCO2 Dissociation Curves at Varied O2, CO2, pH, 2,3-DPG and Temperature Levels17 February 2010 | Annals of Biomedical Engineering, Vol. 38, No. 4The unpretentious role of 2,3-diphosphoglycerate in critical illness*Critical Care Medicine, Vol. 33, No. 10Blood HbO2 and HbCO2 Dissociation Curves at Varied O2, CO2, pH, 2,3-DPG and Temperature LevelsAnnals of Biomedical Engineering, Vol. 32, No. 12Reaction rates of oxygen with hemoglobin measured by non-equilibrium facilitated oxygen diffusion through hemoglobin solutionsBiochimica et Biophysica Acta (BBA) - General Subjects, Vol. 1525, No. 1-2Kinetics of Oxygen and Carbon Dioxide ExchangeDiffusion of Gases Across the Alveolar Membrane1 January 2011Blood Oxygen Transport1 January 2011Oxygen transfer conductance of human red blood cells at varied pH and temperatureRespiration Physiology, Vol. 67, No. 2Effects of Temperature on Oxygen Transfer Conductance of Human Red Blood CellsBlood-gas equilibria, kinetics and transportChemical Engineering Science, Vol. 42, No. 2Blood Gas Transport and 2,3-DPGKinetics of O2 uptake and release by red cells in stopped-flow apparatus: Effects of unstirred layerRespiration Physiology, Vol. 59, No. 1The reaction kinetics of four sheep haemoglobins with identical α-chainsRespiration Physiology, Vol. 53, No. 1Identification of residues contributing to the Bohr effect of human haemoglobinJournal of Molecular Biology, Vol. 138, No. 3Kinetics of Pulmonary Gas ExchangeThe pH Dependence of the Binding of d-Glycerate 2,3-Bisphosphate to Deoxyhemoglobin and Oxyhemoglobin. Determination of the Number of Binding Sites in OxyhemoglobinEuropean Journal of Biochemistry, Vol. 100, No. 2What is the Clinical Importance of Alterations of the Hemoglobin Oxygen Affinity in Preserved Blood - Especially as Produced by Variations of Red Cell 2, 3 DPG Content?Vox Sanguinis, Vol. 34, No. 2The Theoretical Effect of DPG Upon Oxygen Diffusion in Erythrocytes16 April 2012The oxyhemoglobin dissociation curve in health and diseaseThe American Journal of Medicine, Vol. 57, No. 3Kinetics of oxygenation and deoxygenation of erythrocytes containing hemoglobin SRespiration Physiology, Vol. 21, No. 1Influence of altitude training on muscle metabolism and performance in man.British Journal of Sports Medicine, Vol. 8, No. 1The oxygen affinity of axolotl blood and haemoglobin before and after metamorphosisRespiration Physiology, Vol. 18, No. 1 More from this issue > Volume 224Issue 4April 1973Pages 838-847 Copyright & PermissionsCopyright © 1973 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1973.224.4.838PubMed4698800History Published online 1 April 1973 Published in print 1 April 1973 Metrics

Oxygenation properties and 2,3-diphosphoglycerate of human adult and fetal blood.

Oxygen dissociation curves of human adult and cord blood were constructed over a wide range of pH values (5.9-8.7). The cord blood was characterized by a high oxygen affinity as compared with adult blood in the pH region above 6.3. Below that pH region the relationship was reversed.The intracellular pH and 2, 3-diphosphoglycerate (DPG) content of red cells of these two kinds of blood were little different. Upon their incubation at 38°C, both kinds of blood showed an increase in oxygen affinity concomitant with a decrease in the DPG content. From these experiments with the two sorts of blood incubated for various lengths of time it was concluded that the higher oxygen affinity of fetal blood was due mostly to the predominant presence of hemoglobin F, which is not different in oxygen affinity from hemoglobin A but which is quite different in susceptibility to the inhibitory effect of DPG upon oxygen affinity.