Ventricular Diastolic Function in Normal Fetuses and Fetuses with Hb Bart's Disease Assessed by Color M-Mode Propagation Velocity using Cardio-STIC-M (Spatio-Temporal Image Correlation M-Mode)

Purpose: To determine whether ventricular diastolic dysfunction contributes to the pathogenesis of fetal cardiac failure due to fetal anemia using fetal Hb Bart's disease as a live model and cardio-STIC-M as a diagnostic tool. Materials and Methods: Color cardio-STIC volume datasets were acquired from fetuses at risk for Hb Bart's disease during 18 - 22 weeks of gestation and normal pregnancies and pregnancies with hydrops fetalis caused by Hb Bart's disease at 28 - 32 weeks. The volumes were analyzed off-line for velocity propagation (Vp) of the right and left ventricles to assess ventricular diastolic function using color cardio-STIC-M. Results: The Vp for the right and left ventricles was studied in fetuses at 18 - 22 weeks, including 64 normal fetuses (group 1) and 22 fetuses with Hb Bart's disease (group 2), and in fetuses at 28 - 32 weeks, including 22 normal fetuses (group 3) and 16 fetuses with Hb Bart's hydrops fetalis (group 4). The Vp of the fetuses in group 1 and group 2 was not significantly different. However, the Vp for the right and left ventricles in group 4 was significantly lower than in group 3 (19.02 vs. 9.78, p < 0.001; and 20.24 vs. 13.40, p < 0.001, respectively). The inter-observer variability had fair agreement with the intra-class correlation coefficient of 0.531 (95 % CI 0.393 - 0.646, p < 0.001). Conclusion: Hydrops fetalis secondary to fetal anemia is initially caused by hypervolemia rather than ventricular diastolic dysfunction while ventricular diastolic compromise is a late occurring consequence of persistent hypervolemia, different from the mechanism of hydropic changes caused by cardiac causes.

Hb Baden: structural and functional characterization

Hb Baden (β18Val→Met) is a rare variant hemoglobin that has never been functionally or clinically characterized. We describe a Hb Baden heterozygote who exhibits normal growth and development, as well as age- and gender-appropriate hematological values. Surprisingly, in vitro analyses demonstrate that Hb Baden is relatively unstable and exhibits an abnormally high affinity for O₂. These properties are likely to affect the physiologies of individuals who inherit the β(Baden) mutation in trans to a determinant for either a functionally relevant hemoglobinopathy or a mild thalassemia. The data also provide insights into the function of the A-helix/AB-segment of β globin, supporting a structural model in which this poorly understood region serves as a scaffold that fixes the positions of other helices that directly impact β-globin function.

Hb Santa Clara (beta 97His-->Asn), a human haemoglobin variant: functional characterization and structure modelling

This study examines the functional and structural effects of amino acid substitution at alpha(1)beta(2) interface of Hb Santa Clara (beta 97His-->Asn). We have characterized the variation by a combination of electrospray ionisation mass spectrometry and DNA sequence analysis followed by oxygen-binding experiments. Functional studies outlined an increased oxygen affinity, reduced effect of organic phosphates and a reduced Bohr effect with respect to HbA. In view of the primary role of this interface in the cooperative quaternary transition from the T to R conformational state, a theoretical three-dimensional model of Hb Santa Clara was generated. Structural investigations suggest that replacement of Asn for His beta 97 results in a significant stabilization of the high affinity R-state of the haemoglobin molecule with respect to the low affinity T-state. The role of beta FG4 position has been further examined by computational models of known beta FG4 variants, namely Hb Malmö (beta 97His-->Gln), Hb Wood (beta 97His-->Leu), Hb Nagoya (beta 97His-->Pro) and Hb Moriguchi (beta 97His-->Tyr). These findings demonstrate that, among the various residues at the alpha(1)beta(2) (and alpha(2)beta(1)) intersubunit interface, His beta FG4 contributes significantly to the quaternary constraints that are responsible for the low oxygen affinity of human deoxyhaemoglobin.

Low oxygen saturation by pulse oximetry may be associated with a low oxygen affinity hemoglobin variant, hemoglobin Titusville

The authors describe a 10-year-old Caucasian boy who presented with abnormally low oxygen saturation values on pulse oximetry after a routine tonsillectomy. He was asymptomatic and there was no personal or family history of respiratory, cardiac, or hematologic disorders. Multiple initial investigations were completed without diagnostic yield. Eventually, hemoglobinopathy studies identified the presence of a low oxygen affinity hemoglobin variant, characterized as hemoglobin Titusville. Hemoglobinopathies remain highly prevalent worldwide, with more than 65 low oxygen affinity hemoglobin variants identified to date. Early recognition of abnormal hemoglobin variants in asymptomatic patients may avoid extensive, unnecessary medical investigations.

Dominant beta-thalassemia with hemoglobin Hradec Kralove: enhanced hemolysis in the spleen

We describe a 6-year-old girl and her mother with dominant beta-thalassemia due to hemoglobin Hradec Kralove (Hb HK). Both patients presented microcytic anemia, jaundice, splenomegaly, cholelithiasis, and recurrent hemolytic bouts. Osmotic resistance tests using saline and coiled planet centrifugation revealed the increased fragility of the red cell membrane. On the other hand, the glycerol lysing time was prolonged, and results of the isopropanol test were weakly positive. Despite mimicking the features of hereditary spherocytosis, the results of the genetic analyses verified the second reported family with Hb HK (codon 115, GCC [Ala] --> GAC [Asp]). Splenectomy was effective for the amelioration of hemolysis. Of 7 reported patients with Hb variants at beta-globin codon 115 (Hb Madrid and Hb HK), 5 underwent splenectomy. Because of the variable augmentation of extramedullary hemolysis in dominant beta-thalassemias, genotyping is necessary for determining the clinical indication of splenectomy.

Abnormal hemoglobins found in Hunan

OBJECTIVE

To summarize the results of general survey, primary structure analysis and related functional studies of abnormal hemoglobins (Hbs) found in Hunan Province.

DATA SOURCES

International Hb journals, Chinese biochemical and biomedical journals and other articles relevant to hematology.

STUDY SELECTION

All Hb variants found in Hunan and identified by primary structure analysis during 1980 - 1991 were included.

DATA EXTRACTION

Data concerning 11 types of Hb variants found in 3 districts and 7 counties in Hunan Province were briefly documented. Their frequencies of occurrence were calculated and their distributions among Han, Yao, Tujia and Dong ethnic groups were listed.

RESULTS

Thirty-six cases with abnormal Hb were identified out of 7412 individuals screened in Hunan. 11 different types of Hb variants were recognized by primary structure analysis in 19 propositi along with their family members, including 5 alpha-chain variants, 4 beta-chain variants, 1 delta-chain variant and 1 delta-beta chain fusion variant. Oxygen equilibrium characteristics, reaction dynamics, the rate of globin chain synthesis (RGCS), morphology observation by electron microscopy and DNA analysis were all used in the functional studies of hemoglobinopathies.

CONCLUSIONS

The average incidence of abnormal Hbs in Hunan is 0.486%. In Jianghua County, whose inhabitants are mostly of the Yao ethnic group, the incidence is significantly higher (1.09%). Hb Jianghua [beta120(GH3) Lys-->lle] and Hb Shuangfeng (SF) [alpha27(B8) Glu-->Lys] were two new variants first reported in international literature; whereas Hb Lille [alpha74(EF3) Asp-->Ala], HbA(2) Flatbush [delta22(B4) Ala-->Glu] and Hb Lepore-Boston [delta87(F3)-beta116(G18)] were the first three instances to be found in China. Hb SF displayed an oxygen affinity 1.5-fold higher than that of HbA at pH 7.4 and 25 degrees C with its oxygen equilibrium curve shifted to the left. Reticulocytes of Hb SF heterozygote showed unbalanced RGCS, quite similar to that found in beta-thalassemia minor. Erythrocytes of Hb SF heterozygote were changed to spherocytes and began to lyse after incubation with sodium salicylate or sulfadiazine (pH 7.4, 37 degrees C) for 2 - 4 h. These findings explained the sudden attack of hemolytic anemia provoked by two drugs in Hb SF propositus. The genotype of a patient with Hb Q-H disease is identified as -,-/-,alpha(Q) by DNA restriction mapping.

A human embryonic hemoglobin inhibits Hb S polymerization in vitro and restores a normal phenotype to mouse models of sickle cell disease

The principle that developmentally silenced globin genes can be reactivated in adults with defects in beta-globin gene expression has been well established both in vitro and in vivo. In practice, levels of developmental stage-discordant fetal gamma globin that can be achieved by using currently approved therapies are generally insufficient to fully resolve typical clincopathological features of sickle cell disease. The therapeutic potential of another developmentally silenced globin--embryonic epsilon globin--has been difficult to evaluate in the absence of a convenient expression system or an appropriate experimental model. The current work analyzes the antisickling properties of an epsilon -globin-containing heterotetramer (Hb Gower-2) both in vitro as well as in vivo in a well-established mouse model of sickle cell anemia. These animals, expressing 100% human Hb S, display a chronic hemolytic anemia with compensatory marrow and extramedullary erythropoiesis, abundant circulating sickled erythrocytes, and chronic tissue damage evidenced by parallel histopathological and functional deficits. By comparison, related mice that coexpress Hb S as well as Hb Gower-2 exhibit normal physiological, morphological, histological, and functional attributes. Subsequent in vitro analyses substantiate results from whole-animal studies, indicating that the polymerization of deoxygenated Hb S can be significantly slowed by relatively small quantities of Hb Gower-2. Together, the in vivo and in vitro analyses suggest that reactivation of epsilon-globin gene expression would be therapeutically beneficial to adults with sickle phenotypes, and provide a rationale for detailed investigations into the molecular basis for its developmental silencing.

The erythrocyte effects of haemoglobin O(ARAB)

To test the hypothesis that HbOARAB induces an increase in red cell mean corpuscular haemoglobin concentration (MCHC), we studied members of four Tunisian families who were either homo- or heterozygous for HbOARAB or were double heterozygotes for HbS and HbOARAB. The alpha-gene status was also tested. The findings included: (1) Distinctive variation in red cell density (MCHC) as determined by separation of red cells on isopycnic gradients: (a) All red cells from patients homozygous for HbOARAB were denser than normal red cells, as is observed for homozygous HbC patients. (b) In patients heterozygous for HbOARAB, red cell density was strongly influenced by the presence of alpha-thalassaemia. The coexistence of -alpha/alphaalpha resulted in an average red cell density slightly greater than normal (AA) red cells. Patients heterozygous for HbOARAB with a normal complement of four alpha genes had denser red cells similar to sickle cell disease with some cells of normal density but with most cells very dense. (c) Finally, the double heterozygotes for HbS and HbOARAB had significant haemolytic anaemia and red cells denser than normal with some as dense as the densest cells found in sickle cell anaemia. (2) Reticulocytes in patients homozygous for HbOARAB were found in the densest density fraction of whole blood. (3) Cation transport in patients homozygous for HbOARAB was abnormal, with K:Cl cotransport activity similar to that of HbS-Oman and only somewhat lower than in sickle cell anaemia red cells. The activity of the Gardos channel was indistinguishable from that found in HbS, HbC and HbS-Oman cells. We conclude that the erythrocytic pathogenesis of HbOARAB involves the dehydration of red cells due, at least in part, to the K:Cl cotransport system. The similarity of the charge and consequences of the presence of both HbC and HbOARAB, which are the products of mutations at opposite ends of the beta-chain, raises the possibility that this pathology is the result of a charge-dependent interaction of these haemoglobins with the red cell membrane and/or its cytoskeleton and that this abnormality is present early in red cell development.

Low pulse oximeter-measured hemoglobin oxygen saturations with hemoglobin Cheverly

Unexpectedly low hemoglobin oxygen saturation as determined by pulse-oximeter analysis was observed in a patient who underwent an elective surgical procedure. Specific hemoglobin derivatives such as carboxyhemoglobin, methemoglobin, and reduced hemoglobin that have been described to lower pulse-oximetry determination of oxygenation were not detected. Absorbance spectra revealed the patient's hemoglobin to be different than that obtained from two normal volunteers. High-pressure liquid chromatographic analysis of the hemoglobin showed an unknown band that comprised 15% of the patient's hemoglobin. DNA sequence analysis showed a point mutation in the second nucleotide of the 45th codon of the beta-globin chain. This mutation encodes for an abnormal beta-chain (beta-45 Phe-->Ser) that has been described as hemoglobin Cheverly. Hemoglobin Cheverly is an unstable hemoglobin that has a similar mutation as the beta-42 Phe-->Ser mutation seen in hemoglobin Hammersmith. Hemoglobin Hammersmith and another unstable hemoglobin, hemoglobin Köln, have previously been described to have unexpectedly low pulse-oximeter-determined oxyhemoglobin levels. That we find hemoglobin Cheverly to result in a similar phenomenon suggests that pulse-oximeter monitoring of oxygenation status may not be appropriate for the unstable hemoglobins. Low pulse-oximeter oxygenation determinations for these hemoglobins do not appear to predict clinical hypoxemia.

Hb Godavari [alpha 95(G2)Pro-->Thr]: a neutral amino acid substitution in the alpha 1 beta 2 interface that modifies the electrophoretic mobility of hemoglobin

Hb Godavari [alpha 95(G2)Pro-->Thr] was characterized independently in two families of different ethnic origin. The first case, found in the Netherlands, involved an Indian patient. The second one was identified a few months later in an African family from Mali, living in France. Hb Godavari is the fourth example of a substitution involving neutral residues at position alpha 95(G2). In all these variants the electrophoretic pattern suggested that the structural modification unmasks a charged residue buried in the alpha 1 beta 2 contact area. The oxygen affinity of this abnormal hemoglobin was approximately 10% higher than that of Hb A; in the absence of 2,3-diphosphoglycerate, its cooperativity was moderately decreased, suggesting a slightly unstable T state.

Structural and functional studies of hemoglobin Moabit (alpha 86(F7) Leu-->Arg

An abnormal hemoglobin fraction was detected on high performance liquid chromatography profile performed for the measurement of glycated hemoglobin in a 55-year-old caucasian patient. The structural and functional studies were performed by standard techniques. Separation of hemoglobins by alkaline electrophoresis and by IEF revealed a slightly more rapid fraction than does Hb S. By acid electrophoresis, no abnormal Hb fraction could be observed. Separation of globin chains by electrophoresis demonstrated an alpha-chain variant and by chromatography, a fraction which eluted between beta and gamma globin chains. Tryptic digests and amino acid analysis have demonstrated a previously described substitution of Leu-->Arg alpha 86(F7).

Clinical and hematological response to hydroxyurea in a patient with Hb Lepore/beta-thalassemia

The possibility of increasing Hb F in vivo using drugs like 5-azacytidine, hydroxyurea, and butyrate has been established. However, in many cases this does not entail an increase in total hemoglobin. We report on a patient with Hb Lepore/beta-thalassemia being treated with hydroxyurea (30 mg/Kg/day) because of the presence of erythroid extramedullary masses with severe neurological abnormalities. During therapy the patient showed a remarkable improvement in neurological signs due to the reduction in extra-medullary masses, a significant increase in both total hemoglobin (from 5.8 to 9.7 g/dl) and Hb F (from 4.9 g/dl to 9.1 g/dl). The marked improvement in hemoglobin level in our patient with Hb Lepore/beta-thalassemia suggests gamma-globin gene activation due to the DNA structure determined by the crossover event.

Hb T-Cambodia, a beta chain variant with the mutations of Hb E and Hb D-Punjab, confirmed by DNA analysis

Hemoglobin variants with two amino acid substitutions affecting one globin chain are relatively rare. Hb T-Cambodia, a doubly substituted beta-globin variant, was characterized previously by amino acid sequencing as having sequence alterations in beta 26 (beta 8)Glu-->Lys and beta 121(GH4) Glu-->Gln (1). It is a variant that migrates cathodic to Hb A2 on alkaline electrophoresis and with Hb A on acid citrate agar electrophoresis. We report here the mutations of Hb T-Cambodia at the nucleotide level using DNA sequencing, in beta-globin gene codon 121 (GAA-->CAA) and in codon 26 (GAG-->AAG). These are the mutations of Hb D-Punjab and Hb E, respectively.

The structure and function of normal and abnormal haemoglobins

This chapter reviews general aspects of the normal human haemoglobins which include those predominantly present in the embryo, the fetus and newborn baby, and in the normal adult. Special emphasis is given to factors which affect the levels of fetal haemoglobin in the adult because increased percentages of Hb F can be of great benefit to adults with certain haemoglobinopathies such as sickle cell anaemia and beta-thalassaemia. A review of the numerous Hb variants published since the discovery of Hb S in 1959 reveals a steady stream of newly detected abnormalities; most of these are the result of single-point mutations in the alpha-, beta-, gamma-, or delta-globin genes. Of the more than 600 variants listed in a repository, some 200 have clinical significance because of a decreased stability, a change in functional properties, among others. Methodology developed for the detection and quantitation of normal and abnormal Hb components has been greatly modified during the past 30 years; isoelectrofocusing and different fast developing micro chromatographic procedures are the methods of choice. Analyses of DNA isolated from the white cells has become most useful for the final characterization of the variants; this methodology consists of amplification of a desired segment of DNA and identification of a mutation with labelled oligonucleotide probes. Additional methods include sequence determination of this amplified DNA and identification of known mutations with an allele specific amplification procedure.

Hemoglobin Dallas (alpha 97(G4)Asn-->Lys): functional characterization of a high oxygen affinity natural mutant

Hemoglobin Dallas, an alpha-chain variant with a substitution of lysine for asparagine at position 97(G4), was found to have increased oxygen affinity (p1/2 = 1 mmHg at pH 7.3 and 20 degrees C), diminished cooperativity (n, the Hill coefficient = 1.7) and reduced Bohr effect (about 50%). Addition of allosteric effectors (such as 2,3-diphosphoglycerate, inositol hexakisphosphate and bezafibrate) led to a decrease in oxygen affinity and increase in cooperative energy. Kinetic studies at pH 7.0 and 20 degrees C revealed that (i), the overall rate of oxygen dissociation is 1.4-fold slower than that for HbA and (ii), the carbon monoxide dissociation rate is unaffected. The abnormal properties of this hemoglobin variant can be attributed to a more 'relaxed' T-state.

Hemoglobin Neapolis, beta 126(H4)Val----Gly: a novel beta-chain variant associated with a mild beta-thalassemia phenotype and displaying anomalous stability features

A novel beta-chain, beta 126(H4)Val----Gly, electrophoretically silent, was detected by reverse-phase high performance liquid chromatography in three unrelated families from Naples (Southern Italy) and accounted for about 30% of the total beta-chains. The amino acid substitution was detected by HPLC fingerprint. The eight heterozygous patients showed hematologic and biosynthetic alterations of mild beta-thalassemia type. The hemoglobin variant showed abnormal stability features. It was unstable in the heat stability and isopropanol precipitation tests, but did not cause a hemolytic syndrome in vivo and was stable in a time-course experiment of biosynthesis in vitro. DNA polymerase chain reaction direct sequencing of the mutated gene from 135 nt upstream of the cap site to 106 nt downstream of the polyadenylation site showed only the beta 126 GTG----GGG mutation, which was confirmed in the other patients by allele-specific oligonucleotide hybridization. The mutation was found to be associated with a type II beta-globin framework and restriction fragment length polymorphism haplotype V. The novel variant was named hemoglobin Neapolis.

Hemoglobin Warsaw (Phe beta 42(CD1)----Val), an unstable variant with decreased oxygen affinity. Characterization of its synthesis, functional properties, and structure

In Hb Warsaw Val replaces the Phe normally present at the heme contact position beta 42 (CD1). This variant is unstable, and it readily undergoes methemoglobin formation. In DEAE-cellulose chromatography, the variant hemoglobin co-eluted with Hb A; a partially heme-depleted fraction of the variant, representing 5-6% of the total hemoglobin, eluted separately and in pure form. The heme replete form of Hb Warsaw exhibited decreased oxygen affinity with a normal Bohr effect and normal cooperativity and interaction with 2,3-diphosphoglycerate (DPG). The heme-depleted Hb Warsaw had a higher oxygen affinity than that of Hb A, decreased cooperativity and 2,3-DPG interaction, and a very low alkaline Bohr effect. Gel filtration of the heme-depleted form showed it to exist entirely as alpha beta dimers. Globin chain synthesis by Hb Warsaw-containing reticulocytes followed a balanced alpha/beta ratio. In short-term synthesis experiments, a major portion of incorporated radiolabeled L-leucine was recovered from the dimeric, heme-depleted Hb Warsaw fraction, suggesting that subunit association precedes the incorporation of heme into the beta subunits in the post-synthetic assembly of this hemoglobin. Structural analysis of deoxyhemoglobin containing roughly equal proportions of normal and variant beta chains showed that the replacement leaves a cavity next to the heme that is large enough to hold a water molecule, which may account for the instability of Hb Warsaw. The heme and the pyrrol nearest to ValCD1 tilt into the cavity. The resulting increase in the tilt of the proximal histidine relative to the heme plane, coupled with a possible stretching of the Fe-N epsilon bond may account for the low oxygen affinity.

Studies on function of Hb Jianghua [beta 120 (GH3) Lys----Ile]

Hemoglobin Jianghua (Hb Jianghua) is a new fast--moving hemoglobin variant found in China, being named after the county where it was detected. Having its primary structure analysed, we report in this paper the results of studies on its function. The absorption spectrum, response to allosteric effectors and oxygen equilibrium of the chromatographically purified Hb Jianghua showed its characteristics similar to those of purified Hb A. Its alkaline Bohr effect was normal. This indicates that a substitution of isoleucine for the 120th lysine residue of the beta chain had no significant influence upon the function of Hb molecule.

Hb Johnstown [beta 109 (G11) Val----Leu]: a new electrophoretically silent variant that causes erythrocytosis

A high oxygen affinity hemoglobin, previously undescribed, was found in a healthy, asymptomatic patient with mild erythrocytosis and left-shifted hemoglobin-O2 dissociation curve. The hemoglobin variant could not be distinguished from Hb A by any of several electrophoretic methods nor by ion exchange chromatography. It was separated and analyzed by reversed phase high performance liquid chromatography. Structural analysis revealed the substitution beta 109 (G11) Val----Leu. The variant was named Hb Johnstown. The amino acid substitution perhaps disrupts alpha 1 beta 1 contacts in the deoxyhemoglobin conformation, thus shifting the equilibrium towards the high affinity oxyhemoglobin conformation.

Amino-acid sequences and functional differentiation of hemoglobins A and D from swift (Apus apus, Apodiformes)

The blood of the adult swift contains one major (HbA = alpha 2A beta 2) and two minor components (HbD = alpha 2D beta 2 and HbD'). The components were separated by FPLC with a TSK SP-5 PW-column in phosphate buffers, and were eluted with a linear NaCl gradient. HbD' could be detected only in freshly prepared hemolysates with the sensitive FPLC separation method. The globin chains were separated on a cation exchanger (CM-cellulose), the tryptic peptides by HPLC with a RP-2 LiChrosorb column. Their amino-acid sequences were determined by automatic Edman degradation with the film- or gas-phase method. For the alpha A-, alpha D- and beta-chains, peptide alignment was achieved by homologous comparison with the corresponding chains of the greylag goose (Anser anser). The structural significance of the substitutions was examined with the aid of molecular graphics. The oxygen-binding properties of the stripped hemolysate and of HbA and HbD and their dependence on pH, temperature and inositol polyphosphate are presented and discussed with reference to molecular structures and hypothermy that occurs during torpidity.

Hemoglobin Köln occurring in association with a beta zero thalassemia: hematologic and functional consequences

Hemoglobin (Hb) Köln-beta zero thalassemia compound heterozygosity was discovered in a young Greek patient. This gave us the unique opportunity for studying the functional properties of this unstable high-oxygen affinity hemoglobin variant in red cells containing almost pure Hb Köln. The red cells of the proposita exhibit morphological alterations and hematologic indices corresponding to the presence of an unstable Hb and beta thalassemia. Globin chain synthesis confirmed the association with a beta zero thalassemia gene. Oxygen-binding curves for these cells were biphasic, indicating the presence of both heme-saturated and of approximately 20% of non-cooperative Hb Köln. The major component exhibits an increased oxygen affinity, reduced cooperativeness, and normal alkaline Bohr effect. The 35-year-old proposita is active, has not been splenectomized, and has not been transfused in several years.

Pseudosickling of hemoglobin Setif

Hemoglobin Setif produces pseudosickling of red cells in vitro; the nature of the process and the conditions that "trigger" it are unknown. Studies of red cells, hemolysates, purified hemoglobin solutions, and artificial mixtures of Hb A and Setif suggest that pseudosickling is produced by intracellular crystallization of insoluble hemoglobin. Increased tonicity of the suspending medium accentuates the process, probably by causing a rise in intracellular hemoglobin concentration. If precipitates from A/Setif mixtures are analyzed, they always contain Hb A, suggesting an unusual mechanism for the process. Despite the fact that osmolality in the renal medulla is similar to that which produces pseudosickling in vitro, carriers do not have renal dysfunction of the type found in patients with sickle cell disease.

Further characterization of Hb Henri Mondor or alpha 2 beta 2(26)(B8)Glu----Val

A second case of Hb Henri Mondor is reported. The subject, homozygous for Hb Henri Mondor, is of Algerian origin. The electrophoretical behavior and structural characterization are given and discussed. Hb Henri Mondor, which is characterized by the replacement of the lysine residue in position beta 26, as is the case for Hb E, has normal functional properties and is normally expressed.

Erythrocyte membrane deformability and stability: two distinct membrane properties that are independently regulated by skeletal protein associations

Skeletal proteins play an important role in determining erythrocyte membrane biophysical properties. To study whether membrane deformability and stability are regulated by the same or different skeletal protein interactions, we measured these two properties, by means of ektacytometry, in biochemically perturbed normal membranes and in membranes from individuals with known erythrocyte abnormalities. Treatment with 2,3-diphosphoglycerate resulted in membranes with decreased deformability and decreased stability, whereas treatment with diamide produced decreased deformability but increased stability. N-ethylmaleimide induced time-dependent changes in membrane stability. Over the first minute, the stability increased; but with continued incubation, the membranes became less stable than control. Meanwhile, the deformability of these membranes decreased with no time dependence. Biophysical measurements were also carried out on pathologic erythrocytes. Membranes from an individual with hereditary spherocytosis and a defined abnormality in spectrin-protein 4.1 association showed decreased stability but normal deformability. In a family with hereditary elliptocytosis and an abnormality in spectrin self-association, the membranes had decreased deformability and stability. Finally, membranes from several individuals with Malaysian ovalocytosis had decreased deformability but increased stability. Our data from both pathologic membranes and biochemically perturbed membranes show that deformability and stability change with no fixed relationship to one another. These findings imply that different skeletal protein interactions regulate membrane deformability and stability. In light of these data, we propose a model of the role of skeletal protein interactions in deformability and stability.

Hemoglobin Sendagi (beta 42 Phe----Val): a new unstable hemoglobin variant having an amino acid substitution at CD1 of the beta-chain

Hb Sendagi, a new unstable hemoglobin variant, was found in a Japanese male and his daughter, who have a moderate hemolytic anemia. The variant showed decreased stability upon heat and isopropanol precipitation tests. The variant did not separate from hemoglobin A by electrophoresis, but the abnormal beta-chain emerged ahead of the normal beta-chain on reverse-phase HPLC. Structural analyses revealed that the phenylalanine beta 42 (CD1), one of the critical amino acid residues in the heme pocket, had been replaced by valine. Oxygen equilibrium studies of the patient's hemolysates indicated that Hb Sendagi had a lowered oxygen affinity and a normal response to 2,3-diphosphoglycerate. Hb Hammersmith (beta 42 Phe----Ser) and Hb Louisville (Bucuresti) (beta 42 Phe----Leu) have previously been reported to have varying degrees of molecular instability and altered oxygen binding function. Hb Sendagi provides an additional model for elucidation of the role of the phenylalanine beta CD1 on the structure and function of hemoglobin.

Increased phagocytosis of Plasmodium falciparum-infected erythrocytes with haemoglobin E by peripheral blood monocytes

Erythrocytes from subjects with homozygous and heterozygous haemoglobin E (HbE) infected with Plasmodium falciparum in vitro were phagocytosed to a greater extent by normal human monocytes than infected erythrocytes from normal subjects. Susceptibility to phagocytosis was maximal when the parasites developed to trophozoite and schizont stages in both normal and patients' erythrocytes. The increased susceptibility of P. falciparum-infected HbE erythrocytes to phagocytosis by monocytes may play a role in protection against malaria.

Functional activity of the triplicated alpha alpha alpha 4.2/gene rearrangement

Function of the triplicated alpha alpha alpha 4.2/gene rearrangement was assessed by measurement of Hb Bart's and hematological phenotype including alpha/beta biosynthesis ratio. Increased output of alpha globin chains in alpha alpha alpha 4.2/-- compared to alpha alpha/-- was found in a cord blood. In contrast, hematological phenotypes in two family members with the alpha alpha alpha 4.2/-- genotype were consistent with that expected in alpha alpha/--. This would suggest that the additional alpha gene in the alpha alpha alpha 4.2/rearrangement has variable expression.

Pitted red cell counts in sickle cell disease. Relationship to age, hemoglobin genotype, and splenic size

Splenic reticuloendothelial function, as determined by pitted red cell counts in 114 pediatric patients with sickle cell disease, was evaluated. Patients with homozygous sickle cell disease (HbSS) had a mean pit count of 11.8 +/- 7.0% and the count increased with age. Sickle cell hemoglobin C disease (HbSC) patients had a mean pit count of 4.9 +/- 9.1%, the count being unaffected by age. One patient with HbS-beta thalassemia had a count of 12%, while eight patients with HbS-beta + thalassemia had a mean count of 0.4 +/- 0.3%. There was one patient each with HbSS-alpha thalassemia, HbS-O Arab, and HbS-Lepore, and the pit counts were 4.9, 31.4, and 0.4%, respectively. In both HbSS and HbSC patients, the pit count was significantly lower in patients who had palpable spleens. The pit count may be used as a predictor of disease severity in the sickle cell disorders.

Hemoglobin La Desirade alpha A2 beta 2 129 (H7) Ala----Val: a new unstable hemoglobin

Hemoglobin La Desirade is a new unstable hemoglobin variant arising from the substitution of beta 129 (H7) Ala for Val. Hb La Desirade exhibits a low oxygen affinity and normal heme-heme interaction. The variant was found in two unrelated black families in association with Hb S, Hb C or beta o thalassemia.

Hemoglobin Rahere, a human hemoglobin variant with amino acid substitution at the 2,3-diphosphoglycerate binding site. Functional consequences of the alteration and effects of bezafibrate on the oxygen bindings

We encountered an abnormal hemoglobin (Rahere), with a threonine residue replacing the beta 82 (EF6) lysine residue at the binding site of 2,3-diphosphoglycerate, which was responsible for overt erythrocytosis in two individuals of a Japanese family. Hemoglobin Rahere shows a lower oxygen affinity on the binding of 2,3-diphosphoglycerate or chloride ions than hemoglobin A. Although a decrease in the positive charge density at the binding sites of 2,3-diphosphoglycerate in hemoglobin Rahere apparently shifts the allosteric equilibrium toward the low affinity state, it greatly diminishes the cofactor effects by anions. The oxygen affinity of the patient's erythrocytes is substantially lowered by the presence of bezafibrate, which combines with sites different from those of 2,3-diphosphoglycerate in either hemoglobin Rahere or hemoglobin A.

Oxygen binding and stability properties of Hb Santa Ana (beta 88 Leu----Pro)

Hb Santa Ana (beta 88 Leu----Pro) was found at a level of 30% of total hemoglobin in red cells from a patient with congenital hemolytic anemia. Since no detailed functional studies of this hemoglobin have been done previously, we determined oxygen equilibrium curves of red cell suspensions, hemolysates, and isolated Hb Santa Ana. The P50 values obtained were 22.5 mm Hg (37 degrees C, pH 7.4) for red cell suspensions (normal mean = 27.0 mm Hg), 10.0 mm Hg (25 degrees C, pH 7.0) for hemolysate (normal = 13.5 mm Hg), and 1.3 mm Hg (25 degrees C, pH 7.0) for isolated Hb Santa Ana. Measurements of mechanical stability of Hb Santa Ana showed that the oxy-form of this hemoglobin was 10 times more unstable than that of Hb S and 100 times more unstable than that of Hb A. The deoxy-form of Hb Santa Ana was as unstable as its oxy-form, indicating that no stabilization (R----T conversion) takes place upon the deoxygenation of Hb Santa Ana.

Comparison of hemoglobin Köln erythrocyte membranes with malondialdehyde-reacted normal erythrocyte membranes

Splenectomized patients with hemoglobin (Hb) Köln have rigid RBCs with membrane polypeptide aggregates that are not dissociable with disulfide-reducing agents. Malondialdehyde (MDA) action on normal RBCs produced rigid RBCs with similar nondissociable aggregates. To test the hypothesis that Hb Köln RBC aggregates contained unsaturated MDA-type bonds, we reduced normal control RBC membranes, Hb Köln RBC membranes, and MDA-reacted membranes with [3H]NaBH4. Hb Köln RBC membranes and MDA-reacted membranes both had significantly more 3H incorporation than control membranes. Furthermore, 3H incorporation in both Hb Köln and MDA-treated membranes was located in the membrane polypeptide aggregates, presumably saturating the crosslinking bonds. After reaction of RBCs with [14C]MDA, the MDA label was similarly concentrated in the membrane polypeptide aggregates. Normal RBC membranes incubated with MDA were analyzed with and without reduction by NaBH4 prior to amino acid determination by high-performance liquid chromatography (HPLC). Reduction with NaBH4 after MDA treatment decreased the lysyl residues by 33% and the serine by 7% and increased by 10% the methionyl residues, but did not affect 12 other amino acids. Similar changes could be detected in NaBH4-reduced Hb Köln aggregates in methionine and serine content. MDA may also alter protein configuration, as evidenced by an increase in the protease susceptibility of membrane proteins from MDA-treated and Hb Köln RBCs. We conclude that Hb Köln RBC membranes, like MDA-treated membranes, have similar high molecular weight aggregates conferring decreased membrane deformability, [3H]NaBH4-reducible unsaturated bonds, changes in amino acid composition upon reduction, and protease-sensitive configurational changes.

Structure of deoxyhemoglobin Cowtown [His HC3(146) beta----Leu]: origin of the alkaline Bohr effect and electrostatic interactions in hemoglobin

Hemoglobin Cowtown [His HC3(146)-beta----Leu] exhibits high oxygen affinity and a halved alkaline Bohr effect. X-ray analysis shows the COOH-terminal leucine to be in equilibrium between two positions: one with the salt bridge between the terminal carboxyl and Lys C5(40)alpha intact and the leucyl side chain leaning against main chain atoms of helices F and FG and the other with the terminal salt bridge broken and the leucyl side chain touching Pro C2(37)alpha. Structural changes are confined to the immediate neighborhood of the COOH terminus, showing the halving of the alkaline Bohr effect to be due directly to the loss of the histidine, without significant contributions from changes in pK values of other ionizable groups due to structural changes elsewhere.

Functional properties of the whole blood in a carrier of Hb-Atlanta: beta 75 (E-19) Leu-Pro

The Authors illustrate the main functional parameters of the whole blood in a heterozygous carrier of the unstable Hb-Atlanta. The most important results are represented by a right-shifted P50, by a lowered value of n and by an almost normal pH-depending Bohr effect. It is very likely that the first report depends on the relative Hb-A deficiency, whereas the second one could be due to the presence of the unstable Hb. Moreover, the linkage between this latter and DPG would be present.

The effect of bloodletting on exercise performance in a subject with a high-affinity hemoglobin variant

We studied two young army recruits with erythrocytosis. One had a variant hemoglobin with high affinity for oxygen (hemoglobin Osler, also known as Fort Gordon and Nancy, beta 145 Tyr leads to Asp). The other had normal oxygen affinity and erythrocytosis of undetermined etiology. Both were asymptomatic. We studied exercise capacity on a cycle ergometer before and after hemodilution. In the subject with high oxygen affinity, hemodilution resulted in reduced maximal work and increased heart rate at every work level. In addition, minute ventilation and arterial lactic acid increased, while anaerobic threshold decreased, indicating diminished oxygen supply to tissues. In contrast, the subject with normal oxygen affinity had no significant changes in exercise performance after hemodilution. These results suggest that when blood oxygen affinity is high, loss of efficiency in tissue oxygenation can be expected after phlebotomy or hemodilution. Therefore, it may be useful to measure blood oxygen affinity and exercise performance in polycythemic subjects in whom such procedures are intended to ameliorate symptoms of hyperviscosity.

Further studies on the functional properties of hemoglobin M Hyde Park

The oxygen binding properties of Hb M Hyde Park (92 beta, histidine leads to tyrosine) were reinvestigated directing special care to testing the wave length-dependence of the oxygen equilibrium curve and to stabilizing hemoglobin samples using a methemoglobin reductase system. There was no indication that the Hb M Hyde Park fraction separated on a DEAE Sephadex column contained an unknown hemoglobin derivative which appeared in earlier studies. Contrary to earlier observations, there was no significant wave length-dependence of the equilibrium curve of Hb M Hyde Park, verifying the spectrophotometric determination of oxygen saturation. The reductase system satisfactorily reduced the normal alpha chain met hemes without reducing the abnormal beta chain met hemes. The oxygen binding property of Hb M Hyde Park is characterized by 3 to 4 times higher oxygen affinity than that for normal hemoglobin, complete loss of cooperativity, and substantially preserved Bohr effect. These results are consistent in part but not entirely with those observed by earlier investigators. The oxygen affinity of Hb M Hyde Park is between the affinity of the oxy structure and the deoxy structure of normal hemoglobin. Oxygen equilibrium curve of red cell suspension and whole hemolysate containing Hb M Hyde Park were biphasic, indicating that Hb M Hyde Park also exhibited the high oxygen affinity in those samples.

Structural and functional studies of hemoglobin J Cala-bria: beta64 (E8) Gly leads to Asp

A hemoglobin of high electrophoretic mobility was detected in a French male suffering from an acute leukemia; this hemoglobin was also present in his family. The variant was unstable and possessed an abnormal beta chain, in which a glycyl residue in position 64 (E8) was replaced by an aspartyl residue. This variant constitutes a new case of Hb J Calabria. Since the substituted E8 residue is in close spatial contact with that at B6, it was of interest to compare the properties of Hb J Calabria with those of other hemoglobins bearing substitutions at the same site.

Hemoglobin Vancouver [alpha2beta2(73)(E17) Asp replaced by Tyr]: its structure and function

Hemoglobin Vancouver is a new abnormal hemoglobin with an amino acid substitution of the normal aspartyl residue 73 of the beta chain by a tyrosyl residue. It was discovered in a man of Chinese descent in association with beta thalassemia. It was subsequently detected in a sister in association with normal Hb A. The oxygen affinity of the abnormal hemoglobin is decreased but its subunit interaction is normal. The Bohr effect may be slightly increased. This is the fourth abnormal hemoglobin to be found with a substitution at beta73. The others are Hb C-Harlem (alpha2beta2 6Glu replaced by Val and 73 Asp replaced by Asn), Hb Korle-Bu (alpha2beta2 73Asp replaced by Asn), and Hb Mobile (alpha2beta2 73Asp replaced by Val). Although Hb Mobile was found in the present studies to have a decreased affinity for oxygen, Hbs C-Harlem and Korle-Bu have been reported to be normal. These observations of functional differences for variants of beta73 added to earlier observations of the role of the normal beta73 residue to the aggregation of sickle deoxyhemoglobin indicate that this position of the molecule may be important in intra as well as intermolecular interactions.

[Hemoglobin J. Broussais alpha-2 90 Lys leads to Asn beta-2A (FG2) discovered in a Martinique family. Comparison of several analytical technics]

We report a new case of hemoglobin J. Broussais, present in its heterozygote form in a seven year old child from Martinque. The structural characteristics of this abnormal hemoglobin have been compared by three methods: 1. By analytical and preparative finger-printing on silica gel thin layer plates after tryptic digestion. 2. By a programmed separation of tryptic peptides on various ion exchange resins. 3. And by automatic sequencing of the peptides obtained following CNBr cleavage and separation by gel filtration chromatography. The functional behaviour of this hemoglobin was not modified by the substitution of an Asn for a Lys residue at position 90, although its presence induced slight hematological disorders in the patient. Abnormal hemoglobins which have been identified in Martinique and Guadeloupe are reviewed.