Difference In Oxygen Affinity Research Articles

Photocatalytic Synthesis of a Polydopamine-Coated Acellular Mega-Hemoglobin as a Potential Oxygen Therapeutic with Antioxidant Properties.

Hemoglobin-based oxygen carriers (HBOCs) are being developed to overcome limitations associated with transfusion of donated red blood cells (RBCs) such as potential transmission of blood-borne pathogens and limited ex vivo storage shelf-life. Annelid erythrocruorin (Ec) derived from the worm Lumbricus terrestris (Lt) is an acellular mega-hemoglobin that has shown promise as a potential HBOC due to the large size of its oligomeric structure, thus overcoming limitations of unmodified circulating cell-free hemoglobin (Hb). With a large molecular weight of 3.6 MDa compared to 64.5 kDa for human Hb (hHb) and 144 oxygen-binding globin subunits compared to the 4 globin subunits of hHb, LtEc does not extravasate from the circulation to the same extent as hHb. LtEc is stable in the circulation without RBC membrane encapsulation and has a lower rate of auto-oxidation compared to acellular hHb, which allows the protein to remain functional for longer periods of time in the circulation compared to HBOCs derived from mammalian Hbs. Surface coatings, such as poly(ethylene glycol) (PEG) and oxidized dextran (Odex), have been investigated to potentially reduce the immune response and improve the circulation time of LtEc in vivo. Polydopamine (PDA) is a hydrophilic, biocompatible, bioinspired polymer coating used for biomedical nanoparticle assemblies and coatings and has previously been investigated for the surface coating of hHb. PDA is typically synthesized via the self-polymerization of dopamine (DA) under alkaline (pH > 8.0) conditions. However, at pH > 8.0, the oligomeric structure of LtEc begins to dissociate. Therefore, in this study, we investigated a photocatalytic method of PDA polymerization on the surface of LtEc using 9-mesityl-10-methylacridinium tetrafluoroborate (Acr-Mes) to drive PDA polymerization under physiological conditions (pH 7.4, 25 °C) over 2, 5, and 16 h in order to preserve the size and structure of LtEc. The resulting structural, biophysical, and antioxidant properties of PDA surface-coated LtEc (PDA-LtEc) was characterized using various techniques. PDA-LtEc showed an increase in measured particle size, molecular weight, and surface ζ-potential with increasing reaction time from t = 2 to 16 h compared to unmodified LtEc. PDA-LtEc reacted for 16 h was found to have reduced oxygen-binding cooperativity and slower deoxygenation kinetics compared to PDA-LtEc with lower levels of polymerization (t = 2 h), but there was no statistically significant difference in oxygen affinity. The thickness of the PDA coating can be controlled and in turn the biophysical properties can be tuned by changing various reaction conditions. PDA-LtEc was shown to demonstrate an increased level of antioxidant capacity (ferric iron reduction and free-radical scavenging) when synthesized at a reaction time of t = 16 h compared to LtEc. These antioxidant properties may prove beneficial for oxidative protection of PDA-LtEc during its time in the circulation. Hence, we believe that PDA-LtEc is a promising oxygen therapeutic for potential use in transfusion medicine applications.

Bulk volume susceptibility difference between deoxyhemoglobin and oxyhemoglobin for HbA and HbS: A comparative study.

Sickle cell anemia is a blood disorder that alters the morphology and the oxygen affinity of the red blood cells. Cerebral oxygen extraction fraction measurements using quantitative BOLD contrast have been used for assessing inadequate oxygen delivery and the subsequent risk of ischemic stroke in sickle cell anemia. The BOLD signal in MRI studies relies on , the bulk volume susceptibility difference between fully oxygenated and fully deoxygenated blood. Several studies have measured for normal hemoglobin A (HbA). However, it is not known whether the value is different for sickle hemoglobin. In this study, was measured for both HbA and sickle hemoglobin. Six sickle cell anemia patients and 6 controls were recruited. Various blood oxygenation levels were achieved through in vivo manipulations to keep the blood close to its natural state. To account for the differences in oxygen affinity, Hill's equations were used to translate partial pressure of oxygen to oxygen saturation for HbA, sickle hemoglobin, and fetal hemoglobin (HbF) separately. The pH and PCO2 corrections were performed. Temperature and magnetic field drift were controlled for. A multivariate generalized linear mixed model with random participant effect was used. Assuming that is similar for HbA and HbF and that is 5/4 of for HbA, it was found that the values for HbA and sickle hemoglobin were not statistically significantly different from each other. The same value can be used for both types of hemoglobin in quantitative BOLD analysis.

Latent Photoinduced Oxygen Doping Revealed from Emission Saturation of Aggregated Domains in Conjugated Polymer Nanofibers

AbstractPhotoinduced oxidation (doping) of conjugated polymers by complexation with oxygen can have a significant impact on electronic properties and performance in device environments. Nanofiber model forms of poly(3‐hexylthiophene) (P3HT) are investigated using single molecule spectroscopy that possess similar morphological qualities as their bulk thin film counterparts yet, heterogeneity is confined to the spatial dimensions of these particles. Specifically, P3HT nanofibers assembled in anisole solutions contain both aggregated and nonaggregated (amorphous) chains with distinct electronic properties. Excitation intensity dependent photoluminescence (PL) emission imaging is then used to expose differences in oxygen affinity and reactivity upon photoexcitation. Nanofiber regions with low PL yields tend to show faster PL intensity saturation that also degrade much faster following periods of high excitation intensity soaking. Conversely, other regions show gains in PL intensity and virtually no saturation. These PL “gainer” and “loser” behaviors are assigned as originating from amorphous and aggregated P3HT chains, respectively. The apparent propensity of aggregated chains to undergo latent oxygen doping indicates a greater affinity probably due to a larger extent of electronic delocalization in these structures. The results shed new light on degradation factors studied frequently at the bulk material level, which often lacks sufficient sensitivity to specific structural forms.

Mechanisms of Toxicity and Modulation of Hemoglobin-based Oxygen Carriers

ABSTRACTSeveral adverse events have been associated with the infusion of hemoglobin-based oxygen carriers (HBOCs), including transient hypertension, gastrointestinal, pancreatic/liver enzyme elevation, and cardiac/renal injury in humans. Although several mechanisms have been suggested, the basis of HBOC toxicity is still poorly understood. Scavenging of vascular endothelial nitric oxide (NO) and heme-mediated oxidative side reactions are thought to be the major causes of toxicity. However, based on more recent preclinical studies, oxidative pathways (driven by the heme prosthetic group) seem to play a more prominent role in the overall toxicity of free Hb or HBOCs. HBOCs display a diversity of physicochemical properties, including molecular size/cross-linking characteristics leading to differences in oxygen affinity, allosteric, redox properties, and even oxidative inactivation by protein/heme clearing mechanisms. These diverse characteristics can therefore be manipulated independently, leaving open the possibility of engineering a safe and effective HBOC. To date, several antioxidative strategies have been proposed to counteract the redox side reactions of current generation HBOCs.

Species-Specificity in Myoglobin Oxygenation and Reduction Potential Properties

The objective was to compare oxygenation and reduction potential properties of bovine and porcine myoglobins in-vitro. Cyclic voltammetry and homology-based myoglobin modeling were used to determine the species-specific effects on myoglobin reduction potential and oxygenation properties at pH 5.6, 6.4, and 7.4. At all pHs, porcine myoglobin had greater (P = 0.04) oxygen affinity than bovine myoglobin. For both species, oxygen affinity was higher at pH 6.4 > pH 7.4 > 5.6 (P = 0.0002). Myoglobin reduction potential for both species was affected by pH (P < 0.0001). The redox potentials became more negative as pH increased, indicating a proton-coupled electron transfer. There were no differences (P = 0.51) between species in reduction potential properties of heme. Homology-based myoglobin modeling indicated that the porcine myoglobin has a shorter distance between the distal histidine and heme than does bovine myoglobin. The variation in amino acid composition between bovine and porcine myoglobin could be partially responsible for differences in oxygen affinity.

Intraerythrocytic organic phosphates and hemoglobins of skua - Catharacta maccormicki (Stercoraridae): at two different stages of the year in relation to Antartic migration

Catharacta maccormicki blood samples were collected in the winter (October) and in the summer (February) in order to study the intraerythrocytic organic phosphates, hemoglobin (Hb) electrophoretic patterns, oxygen blood equilibrium and stripped Hbs, as well as the effect of 2,3-biphosphoglycerate (BPG) and inositol hexaphosphate (IHP) on oxygen affinity. All the samples (five from the winter and five from the summer) showed the same electrophoretic pattern: one minor fast component and one major slow one. No differences in oxygen affinity and Bohr effect in the samples collected in the winter and in the summer were found. Oxygen affinity was higher in the stripped Hb than in the blood. BPG seemed to have no effect on the functional properties of skua Hb while IHP does. No BPG was found in any sample. Both inositol pentaphosphate (IP5) and IHP were found in all the samples. The IP5/IHP ratio in the winter samples was 3.0 while in summer 3.5. Adenosine diphosphate (ADP) was found in samples from both the seasons. Adenosine monophosphate (AMP) and adenosine triphosphate (ATP) were present only in the summer samples while guanosine triphosphate (GTP) was found in the winter samples. Since IP5 and IHP are very powerful HB allosteric effectors, ATP and GTP might function as other protein modulators.

Dynamic Factors Affecting Gaseous Ligand Binding in an Artificial Oxygen Transport Protein

We report the functional analysis of an artificial hexacoordinate oxygen transport protein, HP7, which operates via a mechanism similar to that of human neuroglobin and cytoglobin: the destabilization of one of two heme-ligating histidine residues. In the case of HP7, this is the result of the coupling of histidine side chain ligation with the burial of three charged glutamate residues on the same helix. Here we compare gaseous ligand binding, including rates, affinities, and oxyferrous state lifetimes, of both heme binding sites in HP7. We find that despite the identical sequence of helices in both binding sites, there are differences in oxygen affinity and oxyferrous state lifetime that may be the result of differences in the freedom of motion imposed by the candelabra fold on the two sites of the protein. We further examine the effect of mutational removal of the buried glutamates on function. Heme iron in the ferrous state of this mutant is rapidly oxidized when exposed to oxygen. Compared to that of HP7, the distal histidine affinity is increased by a 22-fold decrease in the histidine ligand off rate. Electron paramagnetic resonance comparison of these ferric hemoproteins demonstrates that the mutation increases the level of disorder at the heme binding site. Nuclear magnetic resonance-detected deuterium exchange demonstrates that the mutation greatly increases the degree of penetration of water into the protein core. The inability of the mutant protein to bind oxygen may be due to an increased level of water penetration, the large decrease in binding rate caused by the increase in distal histidine affinity, or a combination of the two factors. Together, these data underline the importance of the control of protein dynamics in the design of functional artificial proteins.

Variable oxygen affinity among terrestrial and diving vertebrates

From being the first protein to have its three‐dimensional structure determined to being sequenced for hundreds of species, myoglobin (Mb) has had a distinguished history as a research subject. Although Mb is one of the most studied proteins, surprisingly little is known of its oxygen affinity at physiologically significant temperature or the variability of this oxygen affinity between species. In this study we compared the oxygen affinity (P50) of skeletal muscle Mb from six terrestrial and ten diving vertebrates. After extracting Mb from muscle samples and removing hemoglobin contamination, oxygen affinity was determined using a TCS Hemox Blood Analyzer. We found Mb P50 ranging from 2.5 to 5.3 mmHg at 37°C. Modeling of oxygen transport in muscle tissue will be necessary to determine if this twofold difference in oxygen affinity has significant implications in oxygen transport under various physiological conditions. Variants in Mb structure and function could be adaptive for species that regularly experience muscle hypoxia such as diving vertebrates.

Hb Montfermeil [β 130(H8) Tyr→Cys]: suggests a key role for the interaction between helix A and H in oxygen affinity of the hemoglobin molecule

Hb Montfermeil [β130(H8) Tyr→Cys] is a high oxygen affinity variant causing erythrocytosis. The cysteine replacement is buried in the inside of the β chain where it alters the interactions between helix A and H, with a further effect on helix E. This position has already been proposed to contribute to the difference in oxygen affinity between human and bovine hemoglobins. Three dimensional structural considerations and comparison of the functional behavior of other variants suggest that this region is an important determinant of the intrinsic oxygen affinity of the hemoglobin molecule.

Evaluating the effect of dissolved oxygen on ammonia-oxidizing bacterial communities in activated sludge

The effect of dissolved oxygen (DO) on the communities of ammonia-oxidizing bacteria (AOB) in activated sludge was evaluated in lab-scale and full-scale reactors using the amoA gene as the basis for phylogenetic comparisons. Under controlled laboratory conditions, two chemostats seeded with activated sludge from the same source were operated with high-DO (8.5 mg/L) and low-DO (0.24 and 0.12 mg/L) concentrations for a period of 300 days. At the end of the operation period, the chemostats had enriched AOB communities that belonged to the Nitrosomonas europaea lineage, but were differentiable based on phylogenetic and kinetic analyses. The low-DO chemostat harbored the growth of two different groups within this lineage, differentiable by the amoA sequence comparison and by terminal fragment signatures. The difference in oxygen affinity between high-DO and low-DO enrichments was demonstrated by evaluating the growth kinetics as a function of oxygen concentration. The low-DO enrichment had a higher growth rate at DO concentrations below 4.7 mg/L, but the growth rate significantly decreased at higher DO concentrations, for which the high-DO enrichment experienced higher growth rates. In addition, the dynamic changes in AOB populations in two parallel trains within one full-scale treatment plant were evaluated in response to a significant reduction of DO in one of the treatment trains. Only the train operated with DO concentrations below 1 mg/L favored the establishment of a population of AOB related to the N. europaea lineage.

Comparative Study on the Mechanisms of Partial Oxidation of Methane to Syngas Over Rhodium Supported on SiO2 and γ-Al2O3

A comparative study on the mechanisms of the partial oxidation of methane (POM) to syngas over SiO2- and γ-Al2O3-supported Rh catalysts was carried out using in situ time-resolved FTIR spectroscopy to follow the primary products of POM reaction over the catalysts. Experiments of catalytic performance evaluation and temperature-programmed reduction (TPR) characterization of the catalysts, as well as the in situ FTIR spectroscopic study using CO to probe the oxidation state of Rh species over the catalysts were performed. It was found that the direct oxidation of CH4 to syngas is the main pathway of the POM reaction over Rh/SiO2 catalysts, while the combustion--reforming mechanism is the dominant pathway of syngas formation over Rh/γ-Al2O3 catalysts. The results of TPR characterization indicate that Rh supported on γ-Al2O3 is more difficult to reduce than Rh supported on SiO2. The IR experiments of CO adsorption over Rh/SiO2 and Rh/γ-Al2O3 after the POM reaction reveal that the surface of the Rh/γ-Al2O3 catalyst contains more partially oxidized rhodium (Rh+) species as compared to the Rh/SiO2 catalyst. These results suggest that the significant difference in the mechanisms of the POM reaction over Rh/SiO2 and Rh/γ-Al2O3 catalysts can be related to the difference in the surface concentration of O2- species over the catalysts under the reaction conditions mainly due to the difference in oxygen affinity of the Rh species on the two supports.

High and low oxygen affinity conformations of T state hemoglobin.

To understand the interplay between tertiary and quaternary transitions associated with hemoglobin function and regulation, oxygen binding curves were obtained for hemoglobin A fixed in the T quaternary state by encapsulation in wet porous silica gels. At pH 7.0 and 15 degrees C, the oxygen pressure at half saturation (p50) was measured to be 12.4 +/- 0.2 and 139 +/- 4 torr for hemoglobin gels prepared in the absence and presence of the strong allosteric effectors inositol hexaphosphate and bezafibrate, respectively. Both values are in excellent agreement with those found for the binding of the first oxygen to hemoglobin in solution under similar experimental conditions. The corresponding Hill coefficients of hemoglobin gels were 0.94 +/- 0.02 and 0.93 +/- 0.03, indicating, in the frame of the Monod, Wyman, and Changeux model, that high and low oxygen-affinity tertiary T-state conformations have been isolated in a pure form. The values, slightly lower than unity, reflect the different oxygen affinity of alpha- and beta-hemes. Significantly, hemoglobin encapsulated in the presence of the weak effector phosphate led to gels that show intermediate oxygen affinity and Hill coefficients of 0.7 to 0.8. The heterogeneous oxygen binding results from the presence of a mixture of the high and low oxygen-affinity T states. The Bohr effect was measured for hemoglobin gels containing the pure conformations and found to be more pronounced for the high-affinity T state and almost absent for the low-affinity T state. These findings indicate that the functional properties of the T quaternary state result from the contribution of two distinct, interconverting conformations, characterized by a 10-fold difference in oxygen affinity and a different extent of tertiary Bohr effect. The very small degree of T-state cooperativity observed in solution and in the crystalline state might arise from a ligand-induced perturbation of the distribution between the high- and low-affinity T-state conformations.

The concentration of oxygen species over SiO2-supported Rh and Ru catalysts and its relationship with the mechanism of partial oxidation of methane to synthesis gas

The partial oxidation of methane (POM) to synthesis gas over SiO2-supported Rh and Ru catalysts was studied by in situ microprobe Raman and in situ time-resolved FTIR (TR-FTIR) spectroscopies. The results of in situ microprobe Raman spectroscopic characterization indicated that no Raman band of Rh2O3 was detected at 500 °C over the Rh/SiO2 catalyst under a flow of a CH4/O2/Ar (2/1/45, molar ratio) mixture, while the Raman bands of RuO2 can even be detected at 600°C over the Ru/SiO2 catalyst under the same atmosphere. The experiments of in situ TR-FTIR spectroscopic characterizations on the reactions of CH4 over O2 pre-treated Rh/SiO2 and Ru/SiO2 catalysts indicated that the products of CH4 oxidation over Rh/SiO2 and Ru/SiO2 greatly depend on the concentration of O2− species over the catalysts. On the catalysts with high concentration of O2−, CH4 will be completely oxidized to CO2. However, if the concentration of O2− species over the catalysts is low enough, CH4 can be selectively converted to CO without the formation of CO2. The parallel experiments using in situ TR-FTIR spectroscopy to monitor the reaction of the CH4/O2/Ar (2/1/45, molar ratio) mixture over Rh/SiO2 and Ru/SiO2 catalysts show that the mechanisms of synthesis gas formation over the two catalysts are quite different. On the Rh/SiO2 catalyst, synthesis gas is mainly formed by the direct oxidation of CH4, while on the Ru/SiO2 catalyst, the dominant pathway of synthesis gas formation is via the sequence of total oxidation of CH4 followed by reforming of unconverted CH4 with CO2 and H2O. The significant difference in the mechanisms of partial oxidation of CH4 to synthesis gas over Rh/SiO2 and Ru/SiO2 catalysts can be well related to the difference in the concentration of O2− species over the catalysts under the reaction conditions mainly due to the difference in oxygen affinity of the two metals.

Sexual maturation in turbot (Scophthalmus maximus) is related to genotypic oxygen affinity: experimental support for Pauly's juvenile-to-adult transition hypothesis

The relationships between genotypical differences in oxygen affinity and age at first maturation were investigated. Haemoglobins of 52 turbot were analysed by agar gel electrophoresis and the fish segregated into three genotypes; Hb-I(1/1), Hb-I(1/2), and Hb-I(2/2). The genotype Hb-I(2/2) had the highest oxygen affinity, Hb-I(1/1) the lowest, and that of Hb-I(1/2) lay in between. For both sexes fewer fish of the Hb-I(1/1) and Hb-I(1/2) genotypes matured at 2 years of age compared to the Hb-I(2/2) genotype. The difference was significant only for males. It is concluded that genotypical oxygen affinity properties are related to age at first maturity in turbot, thus lending support to Pauly’s 1984 hypothesis that oxygen supply per unit weight is the master factor in inducing the transition from juvenile to adult in fishes. However, it can not be excluded that sexual maturation in turbot is size determined as Hb-I(2/2) males had higher final weight compared to other genotypes.

Chorioallantoic placentation in squamate reptiles: Structure, function, development, and evolution

AbstractAllantoplacentae in lizards and snakes form during the evolution of viviparity through apposition of the chorioallantois and a vestige of the shell membrane to the uterine lining. Generalized squamate allantoplacentae are epitheliochorial, diffuse, adeciduate, and highly vascular, accomplish maternal‐fetal gas exchange, and possibly transfer small quantities of organic and inorganic nutrients. Placental gas exchange presumably is enhanced by the thinning of tissues lying between fetal and maternal capillaries, a progressive increase in placental vascularity, and in some species, by differences in oxygen affinity of fetal and maternal blood. A few saurian genera (e.g., Chalcides, Mabuya, and Pseudemoia) include species with specialized placentae that transfer large quantities of nutrients. Specializations of the allantoplacentae of these lizards include interdigitating, hypertrophied uterine and chorioallantoic tissues, and enlarged absorptive chorionic epithelia. South American Mabuya are further specialized by the presence of chorionic areolae and a distinctive placentome. Weekes' 1935 classification of placental morphotypes is reviewed, and a few minor modifications are proposed, in addition to recognition of a fourth morphotype. Phylogenetic analyses suggest that placental organs have originated on more than 100 occasions among squamate reptiles, and indicate that three separate lineages have converged on substantial placentotrophy through the evolution of specialized histotrophic placentae. © 1993 Wiley‐Liss, Inc.

Oxygen dependence of redox state of copper in cytochrome oxidase in vitro

To obtain quantitative information about tissue oxygenation from near-infrared signals, the oxygen dependencies of the redox states of both heme a+a3 and copper in cytochrome oxidase of isolated mitochondria were determined at low oxygen concentrations (10(-6)-10(-9) M) using leghemoglobin as an oxygen indicator. The maximum absorbance changes caused by the aerobic-anaerobic transition measured at 830-760 nm of copper in state 3, state 4, and the uncoupled state were 10, 17, and 5% of those at 605-620 nm of heme a+a3, respectively. Thus the relative absorbance ratio of copper to heme a+a3 could be used as a sensitive indicator for the mitochondrial energy state. The oxygen concentrations required for the half-maximal reduction of heme a+a3 varied with the energy state and the respiratory rate and were 7.8 x 10(-8) and 1.6 x 10(-7) M in state 4 and state 3, respectively. In contrast, that of copper was 7.5 x 10(-8) M and was independent of both the energy state and the respiratory rate. The relationship between the percent oxidation of heme a+a3 and copper in the aerobic-anaerobic transition did not show a straight-line relationship. This was referred to as the difference in oxygen affinity between these two chromophores. The deviation from the straight line was larger in state 3 than in state 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical bases for difference in oxygen affinity of maternal and fetal red blood cells of rattlesnakes

Pregnancy in Crotalus viridis oreganus is associated with an increase in the nucleoside triphosphate (NTP) concentration and a concomitant decrease in the oxygen affinity of the adult red blood cell. However, although the red blood cells of non-pregnant adults and fetuses have indistinguishable NTP concentrations, they have different oxygen affinities. Therefore, red blood cell NTP concentrations alone cannot account for the oxygen-affinity difference between fetal and maternal red blood cells. Hemoglobins from adult and fetal snakes had similar intrinsic oxygen affinities; however, adult hemoglobin was more responsive to organic phosphate modulation compared with fetal hemoglobin. Structural differences, indicated by native gel electrophoresis and electrophoresis of the globins under denaturing conditions at high pH, corroborated functional differences of hemoglobins from fetus and adult. Therefore, the biochemical basis for the oxygen-affinity difference between maternal and fetal red blood cells in this rattlesnake appears to be unique. It appears to be caused by a functionally distinct fetal hemoglobin and the pregnancy-associated rise in red blood cell NTP levels in the mother.

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.

Heterogeneity of the hemoglobin of the Ohrid trout (Salmo L. typicus).

We have analyzed the hemoglobins of five individual trout from the Ohrid Lake (Salmo L. typicus) by electrophoretic methods, by reversed-phase high-performance liquid chromatography, and by limited structural analyses. The two major classes of hemoglobin are type I (35% of total) and type IV (65%). Type IV is the major oxygen-transporting hemoglobin; it consists of three types of beta chain (in about equal quantities) and three types of alpha chain (one major and two minor types). Several structural differences have been observed between these three beta (IV) chains and between the three alpha (IV) chains, suggesting a complex genetic system governing the synthesis of these proteins. Moreover, a few amino acid substitutions occur at positions involved in contacts between chains, which suggests that differences in oxygen affinity may exist between these various type IV hemoglobins. Type I hemoglobin is less complex because it contains one type of beta chain and two alpha chains; the latter two differ in numerous positions, suggesting duplications of the alpha (I)-globin gene. The alpha and beta chains of type I hemoglobin differ considerably from the alpha and beta chains of type IV hemoglobin, indicating the existence of alpha (I)- and beta (I)-globin genes separate from the alpha (IV)- and beta (IV)-globin genes.

Maternal-Fetal Oxygen Transfer in Lower Vertebrates

There exists a difference in oxygen affinity between fetal and maternal bloods in almost all vertebrates examined and this difference in affinities probably facilitates oxygen transfer to the fetus. It is likely that the high oxygen affinity of fetal blood represents a biochemical pre-adaptation from an ancestral oviparous embryo for oxygen uptake in a relatively hypoxic environment. In most cases, the maternal-fetal difference in blood oxygen affinities is due to the characteristics of the fetal red cell and not due to any changes in the adult red cell during pregnancy. These characteristics are based on the presence of a unique fetal hemoglobin with an intrinsically high affinity for oxygen or on the absence of high red cell concentrations of organic phosphates—allosteric modulators of hemoglobin function. However, in several species of snake, representing different families, it appears that pregnancy is associated with apronounced decrease in the oxygen affinity of the adult red cell. This suggests that the blood of the pregnant female is better able to unload oxygen to the fetus than could the blood of thenonpregnant adult. The maternal-fetal difference in blood oxygen affinities in these species isprobably due to the characteristics of the fetal red cell as well as to the change in the affinity of the adult cell during pregnancy. Nonetheless, although the magnitude of the pregnancy-associated change in oxygen affinity of the adult cell in these snakes suggests that it is physiologically significant, the actual significance remains to be determined.