Influence of intramolecular cross-links on the molecular, structural and functional properties of PEGylated haemoglobin

The influence of intramolecular cross-links on the molecular, structural and functional properties of PEGylated {PEG [poly(ethylene glycol)]-conjugated} haemoglobin has been investigated. The sites and the extent of PEGylation of haemoglobin by reductive alkylation are not influenced by the presence of an alphaalpha-fumaryl cross-link at Lys-99(alpha). The propylated hexaPEGylated cross-linked haemoglobin, (propyl-PEG5K)(6)-alphaalpha-Hb, exhibits a larger molecular radius and lower colloidal osmotic pressure than propylated hexaPEGylated non-cross-linked haemoglobin, (propyl-PEG5K)(6)-Hb. Perturbation of the haem microenvironment and the alpha1beta2 interface by PEGylation of haemoglobin is reduced by intramolecular cross-linking. Sedimentation velocity analysis established that PEGylation destabilizes the tetrameric structure of haemoglobin. (Propyl-PEG5K)(6)-Hb and (propyl-PEG5K)(6)-alphaalpha-Hb sediment as stable dimeric and tetrameric molecules, respectively. The betabeta-succinimidophenyl PEG-2000 cross-link at Cys-93(beta) outside the central cavity also influences the molecular properties of haemoglobin, comparable to that by the alphaalpha-fumaryl cross-link within the central cavity. However, the influence of the two cross-links on the oxygen affinity of PEGylated haemoglobin are very distinct, indicating that the high oxygen affinity of PEGylated haemoglobin is not a direct consequence of the dissociation of the haemoglobin tetramers into dimers. alphaalpha-Fumaryl cross-linking is preferred to modulate both oxygen affinity and molecular properties of PEGylated haemoglobin, and cross-linking outside the central cavity could only modulate molecular properties of PEGylated haemoglobin. It is suggested that PEGylation induces a hydrodynamic drag on haemoglobin and this plays a role in the microcirculatory properties of PEGylated haemoglobin.     

Separation of glycosylated haemoglobins using immobilized phenylboronic acid. Effect of ligand concentration, column operating conditions, and comparison with ion-exchange and isoelectric-focusing

Haemoglobins from diabetic and non-diabetic individuals have been separated by affinity chromatography using immobilized phenylboronate, which interacts specifically with diol-containing compounds such as glycosylated haemoglobin. The effects of ligand concentration, flow rate, column geometry, preincubation of sample, buffer composition and temperature have been investigated. Significant correlation was found between results from affinity-chromatography and ion-exchange and isoelectric-focusing methods. Isoelectric-focusing of the haemoglobin fractions obtained from affinity chromatography indicate that, in addition to haemoglobin A1c, some haemoglobin A is also bound to immobilized phenylboronic acid. Assays of haemolysates obtained from red blood cells incubated in glucose solutions suggest that unstable pre-(haemoglobin A1c) does not interfere. The assay is not affected by the presence of haemoglobin F.     

Haemoglobins of invertebrate tissues. Nerve haemoglobins of Aphrodite, Aplysia and Halosydna

1. The occurrence of haemoglobin in invertebrate nerves is surveyed. Haemoglobin was observed in the nerves and ganglia of the marine nematode Amphiporus sp. and of the polychaet annelid Halosydna sp. 2. Haemoglobins from the nerve and ganglia of the polychaet annelid Aphrodite aculeata L. and from the nerve of the gastropod mollusc Aplysia californica have been partially purified. The haem in each case was identified as iron protoporphyrin IX. 3. The minimum molecular weight of Aphrodite nerve haemoglobin deduced from the haem content and amino acid analysis is 17090, in agreement with the molecular weight 15600+/-1000 determined by sedimentation equilibrium. 4. The molecular weight of Aplysia nerve haemoglobin was determined by sedimentation equilibrium to be 16400+/-1000. 5. The oxygen dissociation curves are hyperbolic. Half-saturation is achieved at 1.1mm. Hg for Aphrodite nerve haemoglobin and at 4.0mm. Hg for Aplysia nerve haemoglobin. The coefficients for partition between carbon monoxide and oxygen are: Aphrodite nerve haemoglobin, 167; Aplysia nerve haemoglobin, 116. 6. The ferrous haemoglobins combine with cyanide. 7. We conclude that the intracellular haemoglobins of muscle and nerve are similar.     

The thermal denaturation of human oxyhaemoglobins A, A2, C and S

1. The time-courses of thermal denaturation of human oxyhaemoglobins A, A(2), C and S at 45 degrees C were studied by following the increase in protein fluorescence. Haemoglobins S and C were less stable than haemoglobin A, whereas haemoglobin A(2) was considerably more stable. 2. The time-courses of denaturation did not follow first-order kinetics and could be fitted most simply to a co-operative scheme in which the partial denaturation of the alpha chain preceded that of the beta chain. 3. The denaturation of these haemoglobins was studied as a function of temperature by using optical rotatory dispersion. Haemoglobin A(2) was again more stable than the others. The addition of small quantities of haemoglobin A(2) had a disproportionate effect on the stability of haemoglobin C. 4. The thermodynamic parameters of the denaturation process were calculated.     

Heat tolerance,temperature acclimation,acute oxidative damage and canalization of haemoglobin expression in <Emphasis Type="Italic">Daphnia</Emphasis>

Daphnia is a widespread freshwater zooplankton species, which is both a classic and emerging new model for research in ecological physiology, ecotoxicology and evolutionary biology of adaptation to novel environments. Heat tolerance in Daphnia is known to depend both upon evolutionary history of a genotype and on individuals’ acclimation to elevated temperature and to correlate with the level of haemoglobin expression. We demonstrate the existence of north–south gradient of heat tolerance in North American D. pulex, which is not associated with any parallel changes in haemoglobin expression. Geographically distinct clones differ in the way their haemoglobin expression changes due to acclimation to a sub-stressful (28°C) temperature, but these changes are not correlated with the latitude of clones’ origin. Likewise, the effect of acclimation to sub-stressful temperature is independent from, and cannot be fully explained by, haemoglobin expression changes during acclimation. The degree of oxidative damage to haemoglobin, measured as the ratio of absorbance at 540:576 nm at the acclimation temperature, is a strong predictor of 28°C-acclimated Daphnia survival during an acute heat exposure. The comparison of haemoglobin expression in resistant and tolerant clones acclimated to different temperatures indicates that tolerant clones exhibit canalization of haemoglobin expression, possessing a high level of haemoglobin even at non-stressful temperatures. We discuss the evolutionary biology of adaptation and acclimation to elevated temperatures in an ecologically important component of freshwater ecosystems in the context of global climate change.     

Sickle-cell Anaemia,Sickle-cell Thalassaemia,Sickle-cell Haemoglobin C Disease,and Asymptomatic Haemoglobin C Thalassaemia in one Ghanaian Family

A Ghanaian family is described in which a sickle-cell haemoglobin C man married to a sickle-cell thalassaemia woman produced 12 children (eight alive). Four children have sickle-cell anaemia, two sickle-cell haemoglobin C disease, one has sickle-cell thalassaemia, and one is asymptomatic haemoglobin C thalassaemia.It is emphasized that the contribution that adult sickle-cell disease patients make, through procreation, to the persistence of the S gene may be greater than is normally supposed, and that this contribution may soon outstrip that made by balanced polymorphism through falciparum malaria. Widespread haemoglobin genotyping in schools leading to genetic counselling is advocated to decrease the incidence of sickle-cell disease.     

Haemoglobin Rahere (beta Lys-Thr): A new high affinity haemoglobin associated with decreased 2, 3-diphosphoglycerate binding and relative polycythaemia.

A new haemoglobin with increased oxygen affinity, beta82 (EF6) lysine leads to threonine (Hb Rahere), was found during the investigation of a patient who was found to have a raised haemoglobin concentration after a routine blood count. The substitution affects one of the 2, 3-diphosphoglycerate binding sites, resulting in an increased affinity for oxygen, but both the haem-haem interaction and the alkaline Bohr effect are normal in the haemolysate. This variant had the same mobility as haemoglobin A on electrophoresis at alkaline pH but was detected by measuring the whole blood oxygen affinity; it could be separated from haemoglobin A, however, by electrophoresis in agar at acid pH. The raised haemoglobin concentration was mainly due to a reduction in plasma volume (a relative polycythaemia) and was associated with a persistently raised white blood count. This case emphasises the need to measure the oxygen affinity of haemoglobin in all patients with absolute or relative polycythaemia when some obvious cause is not evident.     

Organic phosphates increase the solubility of avian haemoglobin D and embryonic chicken haemoglobin.

The isolated minor haemoglobin fractions (haemoglobin D) of ostrich, chicken and duck haemoglobin, which constitute about 30% of total intracellular haemoglobin, form crystalline aggregates upon deoxygenation at physiological temperature, ionic strength and pH and at haemoglobin concentrations even well below those present in the red cell. The aggregation is reversed by oxygenation, and can be inhibited by addition of organic phosphates or the corresponding major haemoglobin fraction in a stoichiometric ratio of 1:1. Embryonic haemoglobin from chicken has similar characteristics with respect to its solubility. The results indicate close functional homology of alpha D and embryonic pi-chains as well as a novel role for organic phosphates in the regulation of haemoglobin function.     

Phosphate-haemoglobin interaction. The primary structure of the haemoglobin of the African elephant (Loxodonta africana, Proboscidea): asparagine in position 2 of the beta-chain

The primary structure of the haemoglobin of the African Elephant (Loxodonta africana) is reported. The sequence was determined by means of a sequenator. The haemoglobin differs in 26 amino acids in the alpha-chains and in 27 in the beta-chains from that of adult human haemoglobin. The haemoglobin of the African Elephant, like that of the Indian Elephant and Ilama, has only 5 binding sites for polyphosphate. This finding explains the low p(O2)50 value in whole blood as a result of the lower 2,3-bisphosphoglycerate-haemoglobin interaction. This is discussed in relation to aspects of respiratory physiology; some points are also of interest with regard to the Second Punic War and Hannibal's crossing of the Alps.     

Towards a novel haemoglobin-based oxygen carrier: Euro-PEG-Hb, physico-chemical properties, vasoactivity and renal filtration

Blood transfusion is still a critical therapy in many diseases, traumatic events and war battlefields. However, blood cross-matching and storage may limit its applicability, especially in Third World countries. Moreover, haemoglobin, which in red blood cells is the key player in the oxygen transport from lung to tissues, when free in the plasma causes hypertension and renal failure. This investigation was aimed at the development of a novel haemoglobin-based oxygen carrier with low vasoactivity and renal filtration properties. Human haemoglobin was chemically conjugated with polyethylene glycol (PEG) under either aerobic or anaerobic conditions, following different chemical procedures. The resulting PEGylated haemoglobin products were characterized in terms of oxygen affinity, cooperativity, effects of protons and carbon dioxide concentration, and oxidation stability, and were transfused into rats to evaluate vasoactivity and renal filtration. A deoxyhaemoglobin, conjugated with seven PEG and seven propionyl groups, which we called Euro-PEG-Hb, did not produce profound hypertension, was 99% retained within 6 h, and exhibited oxygen binding properties and allosteric effects more similar to human haemoglobin A than the other tested PEGylated haemoglobin derivatives, thus appearing a very promising candidate as blood substitute.     

Histochemical and ultrastructural observations on digestion in Tetrameres fissispina Diesing, 1861 (Nematoda: Spiruridea) with special reference to intracellular digestion

A large proportion of the blood ingested by Tetrameres fissispina is digested extracellularly to haematin. The probable site of extracellular haemoglobin degradation is the glycocalyx of the microvilli which may carry adsorbed enzymes functional in contact digestion. A smaller proportion of the haemoglobin released from haemolysed erythrocytes is endocytosed in an unchanged state by isolated groups of absorptive cells. In the latter, haemoglobin-containing phagosomes apparently fuse with primary lysosomes ultimately to produce large, heterogeneous, multiple phagolysosomes (digestive complexes). Lipid droplets produced during digestion are extruded from these at intervals. Haemosiderin is the end-product of intracellular haemoglobin breakdown—the differences in residues of the extracellular and intracellular processes (haematin and haemosiderin) reflecting differences in the two enzyme systems employed. Haemosiderin is accumulated as sphaerocrystals in dilated cisternae of the ER. It is suggested that the purpose of intracellular digestion is to provide a source of ferric ions (in the form of haemosiderin) for the biosynthesis of endogenous haemoglobin which the extracellular degradation of haemoglobin cannot supply.     

The haemoglobin system of the mudfish, Labeo capensis: adaptations to temperature and hypoxia

The effect of temperature and hypoxic acclimation on the haemoglobin system and intraerythrocytic organic phosphate concentrations in the South African mudfish, Labeo capensis, have been investigated. Exposure to hypoxia or increased temperature raised haemoglobin concentration and decreased NTP/Hb ratio. Temperature acclimation did not effect the oxygenation characteristics of the haemolysate or haemoglobin multiplicity, as evident from isoelectric focussing experiments that showed one cathodic (Hb I) and three anodic haemoglobins (Hb II, III and IV). Oxygen equilibria of the isolated components showed a smaller Bohr effect and lower temperature and organic phosphate sensitivities in the cathodic than in the anodic haemoglobins. Unlike the trout and eel haemoglobin systems, both the anodic and cathodic haemoglobins from L. capensis exhibited sensitivity to organic phosphates but the effect was smaller in the latter. The results indicate that oxygen transport in mudfish blood is supported by variations in the red cell organic phosphate\haemoglobin ratio and the functional differentiation between anodic and cathodic haemoglobins.     

Haemoglobin polymorphism in the Bank vole, Clethrionomys glareolus, in Britain

Three hundred and twenty-two Clethrionomys glareolus from 17 localities in England, Wales and southern Scotland were typed for haemoglobin and two phenotypes were discovered. They have been designated HbS and HbF. The latter is more electronegative at physiological pH. The nature of the molecular difference between the phenotypes was examined and it was concluded that HbF polymerises more readily than does HbS. Haematological investigations showed that although the red cells of animals with HbF contain more potassium, thereby ensuring electrostatic neutrality, there has not been concomitant dilution of the cell contents. It is suggested that the osmotic stress imposed by this high concentration of particles might be reduced by in vivo polymerisation of haemoglobin. HbS was found to predominate in the north of Britain and HbF in the south. As none of the populations sampled contained animals of both types, it is not yet known whether there is a north-south cline in haemoglobin type, or a sharp disjunction.     

Protoporphyrin IX-induced structural and functional changes in human red blood cells,haemoglobin and myoglobin

Protoporphyrin IX and its derivatives are used as photosensitizers in the photodynamic therapy of cancer. Protoporphyrin IX penetrates into human red blood cells and releases oxygen from them. This leads to a change in the morphology of the cells. Spectrophotometric studies reveal that protoporphyrin IX interacts with haemoglobin and myoglobin forming ground state complexes. For both proteins, the binding affinity constant decreases, while the possible number of binding sites increases, as the aggregation state of the porphyrin is increased. The interactions lead to conformational changes of both haemoglobin and myoglobin as observed in circular dichroism studies. Upon binding with the proteins, protoporphyrin IX releases the heme-bound oxygen from the oxyproteins, which is dependent on the stoichiometric ratios of the porphyrin: protein. The peroxidase activities of haemoglobin and myoglobin are potentiated by the protein-porphyrin complexation. Possible mechanisms underlying the relation between the porphyrin-induced structural modifications of the heme proteins and alterations in their functional properties have been discussed. The findings may have a role in establishing efficacy of therapeutic uses of porphyrins as well as in elucidating their mechanisms of action as therapeutic agents.     

Studies on haemoglobin immobilized by cross-linking with glutaraldehyde. Cross-linked soluble polymers and artificial membranes

Human haemoglobin was immobilized by cross-linking with glutaraldehyde as soluble polymers and artificial membranes. Effects of pH and 2,3-diphosphoglycerate on oxygen binding and cross-linking were studied with haemoglobin immobilized in both the oxy and deoxy states. The cooperativity is suppressed and the affinity is increased when compared with native haemoglobin. Haemoglobin immobilized in the oxy state exhibited a higher oxygen affinity than that immobilized in the deoxy state. The alkaline Bohr effect is not significantly different from that of native haemoglobin. The 2,3-diphosphoglycerate influence on oxygen binding was reduced by one third with immobilization. In order to separate the chemical and the "conformation freezing' effects on the properties of immobilized haemoglobin, glutaraldehyde-modified haemoglobin in oxy and deoxy states was produced. Oxygen binding was studied and chemical modifications were checked by electrophoresis and gel filtration. This chemically modified haemoglobin without polymerization and without intra-chain bridging exhibits a behaviour similar to that of cross-linked soluble polymers or membranes of haemoglobin.     

Whale (Balaenoptera physalus) haemoglobin: primary structure,functional characterisation and computer modelling studies

The functional properties of haemoglobin from the Mediterranean whale Balaenoptera physalus have been studied as functions of heterotropic effector concentration and temperature. Particular attention has been given to the effect of carbon dioxide and lactate since the animal is specialised for prolonged dives often in cold water. The molecular basis of the functional behaviour and in particular of the weak interaction with 2,3-diphosphoglycerate is discussed in the light of the primary structure and of computer modelling. On these bases, it is suggested that the A2 (Pro-->Ala) substitution observed in the beta chains of whale haemoglobin may be responsible for the displacement of the A helix known to be a key structural feature in haemoglobins that display an altered interaction with 2,3-diphosphoglycerate as compared with human haemoglobin. The functional and structural results, discussed in the light of a previous study on the haemoglobin from the Arctic whale Balaenoptera acutorostrata, give further insights into the regulatory mechanisms of the interactive effects of temperature, carbon dioxide and lactate.     

Haematological parameters in a neotropical fish, Corydoras paleatus (Jenyns, 1842) (Pisces, Callichthyidae), captured from pristine and polluted water

We report normal ranges of haematological indices in healthy Corydoras paleatus from an unpolluted area. Haematological parameters studied include: erythrocyte counts (Er), haematocrit (Ht), haemoglobin concentration (Hb), mean cell volume (MCV), mean cell haemoglobin (MCH) and mean cell haemoglobin concentration (MCHC). Normal red blood parameters did not change according to maturation stages, sex or seasons. Then, we compared them with those coming from fish captured in a site polluted by sewage. Fish exposed to pollution presented significantly higher values of Er, Ht, Hb, MCH and MCHC than those captured in an unpolluted area. Discriminant analysis showed that Hb is a key parameter to point out differences between populations exposed to different environmental conditions. We suggest that haematological values of C. paleatus, registered during this study, could be used as biomarkers in future works evaluating the incidence of environmental stress on fish as well as pointing out changes in the water quality.     

Studies on blood components of an air-breathing siluroid fish, Heteropneustes fossilis (Bloch) in relation to body weight.

Different haematological parameters have been studied in relation to the body weight of Heteropneustes fossil (Bloch). The erythrocytes and leucocytes number and haemoglobin concentration increases from lower to higher weight groups. The heart weight also increases along with other blood components. With the unit increase in the body weight of this fish, the heart weight, erythrocytes, leucocytes and haemoglobin increase by a fractional power of 0.85700, 0.13480, 0.13215 and 0.22876, respectively. This shows that haemoglobin increases at a higher rate than erythrocyte number. The coefficient of correlation between body weight and erythrocyte (r = 0.70015), leucocytes (r = 0.95861), haemoglobin (r = 0.96615) and heart weight (0.97577) indicate high degree of correlation. The erythrocytes and leucocytes count and haemoglobin concentration per gram body weight is higher in younger fishes and decrease as the animal grows in size. The haematocrit values and mean corpucsular volumes decrease from lower to higher weight groups, whereas mean corpuscular haemoglobin concentration increases with body weight. The erythrocyte cell surface has a decreasing trend from lower to higher weight group. Due to difference in the rate of decrease of greatest and least diameter of erythrocytes, the elliptical shape of R.B.C. which is common in younger animals, becomes circular in higher weight group. The non-granulocytes increase constantly while the percentage of granulocytes decreases from lower to higher weight groups. The lymphocytes constitute the main bulk of all the leucocytes. The total lymphocytes also increase with the body weight. Spindle cells and monocytes are relatively less in numbers. The percentage of eosinophils, basophils and neutrophils also decrease from lower to higher weight groups.     

Effects of waterborne iron on growth, reproduction, survival and haemoglobin in Daphnia magna

The effects of waterborne iron (FeCl3 X 6H2O) on growth, reproduction, survival and haemoglobin content in Daphnia magna were studied from subnormal to toxic concentrations in hard reconstituted water. Low concentrations of iron stimulated reproduction and haemoglobin synthesis after chronic exposure for 21 days. Maximum reproduction occurred between 0.1 and 1 microgram Fe 1(-1). Juvenile growth was not stimulated by iron but was slightly inhibited between 1 and 8 micrograms Fe 1(-1) and above 128 micrograms Fe 1(-1). A slight inhibition of growth persisted for 21 days. Total haemoglobin content was above the control with no waterborne iron at all but one concentration (512 micrograms Fe 1(-1]. The highest value (3.8 X control value) was found at 2 micrograms Fe 1(-1). The haemoglobin content decreased between 64 and 512 micrograms Fe 1(-1) and increased at higher concentrations. The decrease coincided with an inhibited reproduction. The increase was found in non reproductive survivors. A comparison with a previous study in D. magna suggests that ambient conditions (hardness and pH) and ageing of the water are important for the effects of waterborne iron. At a hardness of 250 mg 1(-1) as CaCO3 and a pH range of 7.0-8.0 the ZEP (Zero Equivalent Point) for reproduction was 158 micrograms Fe 1(-1). Continuous exposure to higher concentrations is expected to lead to extinction of a D. magna population.     

Haemoglobins of the shark, Heterodontus portusjacksoni. III. Amino acid sequence of the beta-chain

The amino acid sequence of the beta-chain of the principal haemoglobin from the shark H. portusjacksoni has been determined. The chain has 141 residues, the same as that of mammalian alpha-chains and less than the 146 residues of mammalian beta-chains or the 148 residues of the alpha-chain from the tetrameric shark haemoglobin. The sequence was deduced from the sequences of peptides obtained by digestion of the globin or its cyanogen bromide fragments with trypsin, chymotrypsin, pepsin and papain. The difference in length of the beta-chain is most readily accounted for by the absence of the D helix. This small helical section is normally present in myoglobins and beta-globins but absent in alpha-chains. The deduction that it is absent from shark beta-chain is based on consideration of homology. The beta-chain shows the insertion of histidine beta2 and the deletions corresponding to residues A17 and AB1 relative to alpha-and myoglobin chains. The reactive thiol group in shark haemoglobin was shown by radioactive labelling to be residue 51 in the beta-chain, immediately preceding the E helix. The amino acid sequence of shark beta-chain shows 92 differences from human beta-chain, significantly more differences than shown by chicken or frog beta-chains, in line with its earlier time of divergence. If the tertiary structure of the shark beta-chain is the same as that of the horse then there are two changes in the alpha1beta2 contact site in oxyhaemoglobin and an additional one in deoxyhaemoglobin. When both alpha- and beta-chain contacts are considered there is a total of nine changes in residues involved in the alpha1beta2 contacts. There is no Bohr effect in shark haemoglobin, and of the residues normally involved in this effect the C-terminal histidine residue of the beta-chain is present, but the aspartyl (FG1) residue to which it is salt-linked is not, being replaced by a glutamyl residue.