Effect of heat on the circular dichroism of spectrin in hereditary pyropoikilocytosis

Effect of xylose on the structural and physicochemical properties of peanut isolated protein based films

PPI films incorporated with xylose were prepared. Addition of xylose increases tensile strength and elongation, and reduces solubility of the film. Films had more homogeneity and denser structure with the addition of xylose 10%.

Erythrocyte membrane defects in hemolytic anemias found through derivative thermal analysis of electric impedance

Hereditary hemolytic anemias originate mainly from defects in hemoglobin and plasma membrane proteins. Here, we propose a new method, thermal analysis of impedance, sensitive to membrane defects. It detects three processes in erythrocyte membrane; fall in membrane capacity at 49.5 degrees C and activation of passive PO(4)(2+) permeability at 37 degrees C and inorganic ions at 61.5 degrees C. The denaturation of spectrin is involved in the first process whilst the anion channel is involved in latter processes. Using this method three persons with xerocytosis were found whereby the fall in membrane capacity and spherization of erythrocytes were both postponed (53 degrees C) compared to control (49.5 degrees C). In contrast to control cells, strong activation of passive permeability for Cl(-) at 37 degrees C and sucrose at 61 degrees C were detected that were both eliminated by pre-inhibition of the anion channel with 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS). In addition, erythrocytes from 15 patients with various forms of anemia were studied in intact state and after refreshment. The results were compared with the data of clinical laboratory and osmotic fragility test. The final conclusion is that this method detects membrane defects with altered spectrin and anion channel syndrome (hereditary xerocytosis, spherocytosis, poikilocytosis and pyropoikilocytosis, elliptocytosis and stomatocytosis) and, after refreshment, helps differentiate them from the anemia with hemoglobinopathy.

Hereditary elliptocytosis: spectrin and protein 4.1R

Hereditary elliptocytosis (HE) is a common disorder of erythrocyte shape, occurring especially in individuals of African and Mediterranean ancestry, presumably because elliptocytes confer some resistance to malaria. The principle lesion in HE is mechanical weakness or fragility of the erythrocyte membrane skeleton due to defects in alpha-spectrin, beta-spectrin, or protein 4.1. Numerous mutations have been described in the genes encoding these proteins, including point mutations, gene deletions and insertions, and mRNA processing defects. Several mutations have been identified in a number of individuals on the same genetic background, suggesting a "founder effect." The majority of HE patients are asymptomatic, but some may experience hemolytic anemia, splenomegaly, and intermittent jaundice.

Hyperthermia, unlike ionizing radiation and chemical oxidative stress, does not stimulate proteolysis in erythrocytes

1. Oxidative stress by phenazine methosulfate stimulated proteolysis in erythrocytes. 2. Gamma-irradiation of erythrocytes in the range of 50-1000 Gy also resulted in the induction of proteolysis. 3. Though it has been suggested that hyperthermia imposes an oxidative stress on a cell, hyperthermic exposure of erythrocytes (30 min, 39-49 degrees C) did not stimulate proteolysis during subsequent incubation of whole cells or hemolysates. 4. Proteolytic degradation of spectrin was accelerated during incubation of membranes isolated from cells heated above 45 degrees C but this effect seems to be due rather to thermal denaturation of spectrin than to oxidative modification of cellular proteins by hyperthermia.

Relationship of hyperthermia-induced hemolysis of human erythrocytes to the thermal denaturation of membrane proteins

Hemolysis of human erythrocytes as a function of time of exposure to 47.4-54.5 degrees C was measured and correlated to thermal transitions in the membranes of intact erythrocytes as determined by differential scanning calorimetry (DSC). Curves of hemoglobin leakage (a measure of hemolysis) as a function of time have a shoulder region exhibiting no leakage, indicative of the ability to accumulate sublethal damage (i.e., damage not sufficient to cause lysis), followed by a region of leakage approximating pseudo-first-order kinetics. Inverse leakage rates (Do) of 330-21 min were obtained from 47.4-54.5 degrees C, respectively. A relatively high activation energy of 304 +/- 22 kJ/mol was obtained for leakage, eliminating the involvement of metabolic processes but implicating a transition as the rate-limiting step. Membrane protein involvement was suggested by the very low rate (10(-2) of the rate from erythrocytes) and low activation energy (50 +/- 49 kJ/mol) of hemoglobin leakage from liposomes containing no membrane protein. A model was developed that predicts a transition temperature (Tm) for the critical target (rate-limiting step) of 60 degrees C when measured at a scan rate of 1 K/min. DSC scans were obtained from intact erythrocytes and a procedure developed to fit and remove the transition for hemoglobin denaturation which dominated the scan. Three transitions remained (transitions A, B, and C) with Tm values of 50.0, 56.8, and 63.8 degrees C, respectively. These correspond to, but occur at slightly different temperatures than, the A, B, and C transitions of isolated erythrocyte membranes in the same salt solution (Tm = 49.5, 53-58, and 65.5 degrees C, respectively). In addition, the relative enthalpies of the three transitions differ between isolated membranes and erythrocytes, suggestive of membrane alterations occurring during isolation. Thus, all analyses were conducted on DSC scans of intact erythrocytes. The B transition is very broad and probably consists of several transitions. An inflection, which is seen as a distinct peak (transition B3) in fourth-derivative curves, occurs at 60.8 degrees C and correlates well with the predicted Tm of the critical target. Ethanol (2.2%) lowers the Tm of B3 by 4.0-4.5 K, close to the shift of 3.3 K predicted from its effect on hemolysis. Glycerol (10%) has very little effect on both hemolysis and the Tm of B3, but it stabilizes spectrin (delta Tm = 1.5 K) against thermal denaturation.(ABSTRACT TRUNCATED AT 400 WORDS)

Spectrin autoantibodies in normal human serum and in polyclonal blood grouping sera

Naturally occurring spectrin autoantibody was detected in normal human sera and in polyclonal blood grouping sera by the immunoblotting technique. The autoantibody seems to be IgG, stable, of high titre and low affinity. It was detected in all sera tested. Preparations of monoclonal antibodies directed against some blood group antigens and anti-A1 lectin reagent were devoid of spectrin autoantibody as expected. This autoantibody may be instrumental in clearing red cell membrane components from the circulation during haemolysis. Care must be exercised in studies designed to determine the association of some blood group antigens with the red cell membrane skeleton, when using polyclonal sera which contain spectrin autoantibodies in addition to the antibodies against the blood group antigen in question.

Heat-induced dissociation of human erythrocyte spectrin dimer into monomers

Human erythrocyte spectrin heated above 49 degrees C could be separated into two fractions by DEAE-Toyopearl column chromatography at room temperature. The first fraction eluting with the salt gradient was predominantly the alpha subunit, indicating a heat-induced dissociation of the spectrin alpha beta dimer into monomers. The second fraction, obtained with 0.5 M NaOH after salt elution, consisted of high-molecular-weight proteins in addition to alpha and beta subunits, which were visualized by gel electrophoresis with sodium dodecyl sulfate. The isolated beta subunit when heated above 48 degrees C could also be separated into two fractions by column chromatography. About 30% of the protein eluted with the salt solution and the rest of the proteins were in the alkali eluate in which high molecular weight protein bands also appeared, indicating a heat-induced aggregation of the beta subunits. Almost all the isolated alpha subunit, however, eluted out with the salt solution, even though the subunit was heated at 52 degrees C. Studies of the binding of subunits to inside-out vesicles indicate that the isolated beta subunit was denatured irreversibly by heating; on the other hand, the alpha subunit kept its binding ability after heating above 50 degrees C. These findings are attributed to the heat-induced dissociation of the spectrin molecules into alpha and beta subunits at 49-50 degrees C, and eventual aggregation of the denatured beta subunits.

Hereditary elliptocytosis, spherocytosis and related disorders: consequences of a deficiency or a mutation of membrane skeletal proteins

The membrane skeleton, a protein lattice that laminates the internal side of the red cell membrane, contains four major proteins: spectrin, actin, protein 4.1 and ankyrin. By mass, the most abundant of these proteins is spectrin, a fibre-like protein composed of two chains, alpha and beta, which are twisted along each other into a heterodimer. At their head region, spectrin heterodimers are assembled into tetramers. At their distal end, these tetramers are interconnected into a two dimensional network by their linkage to oligomers of actin. This interaction is greatly strengthened by protein 4.1. The skeleton is attached to the membrane by ankyrin, a protein that connects the spectrin beta chain to the major transmembrane protein band 3, the anion channel protein. Additional attachment sites are those of protein 4.1 with several glycoproteins, namely glycophorin A and C, as well as direct interactions between spectrin, protein 4.1 and the negatively charged lipids of the inner membrane lipid bilayer. Hereditary spherocytosis, elliptocytosis and pyropoikilocytosis represent a group of disorders that are due to deficiency or dysfunction of one of the membrane skeletal proteins (Fig. 1). Known deficiency states include that of spectrin, ankyrin and protein 4.1. Severe spectrin and ankyrin deficiencies (with decrease in spectrin and ankyrin contents to about 50% of the normal amount) are both rare disorders associated with severe autosomal recessive hereditary spherocytosis. On the other hand, mild spectrin deficiency is found in the majority of patients with autosomal dominant spherocytosis in which the degree of spectrin deficiency correlates with the clinical severity of the disease. Protein 4.1 deficiency, in contrast, is associated with hereditary elliptocytosis, which in certain populations constitutes about 20% of all such patients. Known skeletal protein dysfunctions include mutants of both alpha and beta spectrin that involve the spectrin heterodimer self-association site. These are clinically expressed as hereditary elliptocytosis (HE) and a closely related disorder, hereditary pyropoikilocytosis (HPP). At the level of protein function, this defect can be detected by analysis of the content of spectrin dimers and tetramers in 0 degrees C low ionic strength extracts of red cell membranes. Their structural identification is accomplished by limited proteolytic digestion of spectrin followed by two-dimensional tryptic peptide mapping.(ABSTRACT TRUNCATED AT 400 WORDS)

Mutant forms of spectrin alpha-subunits in hereditary elliptocytosis

Two variant spectrins have been described in hereditary elliptocytosis (HE) and pyropoikilocytosis (HPP). Both are characterized by increased susceptibility of the alpha I (N-terminal) 80-kD domain to mild tryptic digestion, yielding peptides of 46-50 or 65-68 kD (T50a and T68 in our terminology). In this report we add a third unstable spectrin alpha I domain found in three kindreds with HE; alpha IT80 in this type of spectrin is cleaved by mild tryptic digestion to a 50-kD peptide (T50b) distinguished from T50a by its more basic isoelectric point. All three spectrins show impaired self-association to form oligomers. Intermediate tryptic peptides of the three unstable alpha I domains from HE spectrins were characterized by monoclonal immunoblotting and I125 limit peptide mapping and affinity purified using polyclonal anti-alpha IT80. Partial amino acid sequences of alpha I domain peptides were obtained from two unrelated patients for each of the three variant spectrins. T50a results from cleavage at arginine 250 or lysine 252 of alpha IT80; a proline replaced the normal leucine or serine at residues 254 and 255, respectively. T50b and a 19-kD peptide result from cleavage at arginine 462 or arginine 464; a proline replaced the normal residue 465 (in T19b) in one of the two patients studied. T68 results from cleavage at arginine 131. In both 68-kD peptides examined, a leucine is inserted at residue 150. The relationship of the sequence changes to the new tryptic cleavages, to the current model of alpha I domain structure, and to defective spectrin self-association is discussed.

Conformation similarities of the globular and tailed forms of acetylcholinesterase from Torpedo californica

The conformation of the globular dimer (G2), the tailed asymmetric dodecamer (A12, also containing some tailed octamer A8) and the globular tetramer (G4, prepared by removing the collagen-like tail from A12) of acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) was studied by circular dichroism (CD) in the ultraviolet region. The G2 and G4 forms had similar conformation with about 40% alpha-helix, 35% beta-sheets and 4% beta-turns; the tailed form had a lower helicity (about 34%) and beta-form (about 25%) content probably because of the presence of the tail whose CD spectrum resembles that of an unordered form, but it had about the same amount of beta-turns as the other two forms. All three forms also had similar CD spectra in the near-ultraviolet region due to their non-peptide chromophores. The pH, thermal and urea denaturation of the three acetylcholinesterase forms was also similar to each other. The pH-dependency of both the enzymatic activity and CD intensity of the three forms showed bell-shaped curves with a plateau at pH 7-8. The activity was completely lost at pH below 5 or above 10, but the corresponding CD spectra retained 70-80% of the original magnitudes. Thermal denaturation of the three forms at pH 7.5 showed a conformational transition and loss of activity between 30 and 40 degrees C, but the CD intensity of the helical band at 222 nm was reduced by only 20-30%. Urea denaturation of the three forms began at 1 M urea; it was protein concentration- and time-dependent. Again, the activity disappeared faster than the decreasing CD intensity. Thus, the overall conformation of the three acetylcholinesterase forms appears to be relatively stable, but their active site is easily perturbed by changing the environment. The loss of activity correlated well with the disappearance of the CD band of tryptophan(s) in the near-ultraviolet region, suggesting that the Trp residue(s) might be at or near the active center of the enzyme.

Prenatal diagnosis of hereditary red cell membrane defect

The red cells of a severely anaemic 2-year-old child of a white British family showed high haemolytic fragility with poikilocytosis. The cells showed markedly impaired thermal stability. The mother was phenotypically normal, but the father's red cells showed mild elliptocytosis. The spectrin from the latter, extracted at low temperature, was 30% dimeric (cf. 5-10% in normals). Tryptic digests of the spectrin from both father and daughter showed a reduction in the fragment of 80,000 molecular weight, derived from the terminus of the alpha-chain, and the elevation of a fragment of molecular weight 46,000, as well as one of 53,000. These characteristics and the autosomal recessive inheritance lead to a diagnosis of type II hereditary pyropoikilocytosis, so far reported only in two black American families (Lawler et al, 1983). The spectrin from the father was examined with respect to thermal conformational stability, and was found to be normal. The spectrin from the cells of the daughter gave evidence of the presence of oxidative (disulphide) cross-links, as well as of extensive noncovalent aggregation. Blood was obtained from the umbilical cord vein of the 19-week fetus of the pregnant mother: 250 microliters of blood was used for preparation of red cell membranes for SDS-gel electrophoresis and for extraction of spectrin. Analysis of the spectrin by gel electrophoresis in the native state revealed that the proportion of dimer was within the normal range, and the fetus therefore did not possess the hereditary pyropoikilocytosis phenotype. It is suggested that the procedures described could be generally applied to the prenatal identification of phenotypes associated with severe haemolytic anaemias.

Altered spectrin association and membrane fragility without abnormal spectrin heat sensitivity in a case of congenital hemolytic anemia

In hereditary pyropoikilocytosis (HPP) and one type of hereditary elliptocytosis (HE), spectrin self-association is abnormal [5,7]. Spectrin extracted from normal erythrocyte membranes at 0 degree C is nearly all tetrameric, while in HPP and HE (type 1) a substantial amount of the extracted spectrin is dimeric. Abnormal reassociation of spectrin dimers to tetramers can also be demonstrated. We here report the case of a family in which the child has moderately severe hemolysis, with extreme microcytosis and poikilocytosis. The spectrin extracted at 0 degree C was predominately dimer. Parents had levels of dimer intermediate between patient and control values. The temperature dependence was normal for erythrocyte fragmentation; spectrin extractability; and circular dichroism of purified spectrin. Neither the patient nor either parent had elliptocytic red cells as judged from smears and scanning electron microscopy. The presence of substantial amounts of dimeric spectrin in the parents is consistent with a model in which each parent is heterozygous for a different nonassociating mutant spectrin, while the child has inherited a nonassociating molecule from each parent. In each individual, the degree of mechanical stability of the erythrocyte membrane, determined by ektacytometry, was proportional to the amount of tetramer found in the membrane. The description of this case is consistent with either HPP or a form of homozygous HE which is asymptomatic in the carrier state.

Abnormal transbilayer mobility of phosphatidylcholine in hereditary pyropoikilocytosis reflects the increased heat sensitivity of the membrane skeleton

We determined whether the membrane defect in hereditary pyropoikilocytosis (HPP) is associated with thermally induced changes in the lipid bilayer, the stability of which was probed by the rate of translocation of phosphatidylcholine (PC) over the two leaflets. [14C]PC was incorporated into the outer leaflet of the lipid bilayer of the intact erythrocytes using a PC-specific phospholipid exchange protein. The transbilayer equilibration of this PC was determined by measuring the time-dependent changes in its accessibility to exogenous phospholipase A2. The rate of transbilayer equilibration of PC was increased in HPP cells at 37 degrees C when compared to normal erythrocytes (rate constants, 0.07 +/- 0.02 and 0.03 +/- 0.01 h-1, respectively). A further dramatic increase in PC transbilayer equilibration was noted in HPP cells incubated at 44 degrees C (rate constant, 0.15 +/- 0.02 h-1). A similar marked acceleration in transbilayer movement of PC was also seen in normal erythrocytes when incubated at 46 degrees C (rate constant, 0.13 +/- 0.03 h-1). Despite the enhanced transbilayer mobility of PC in HPP cells when compared to normal erythrocytes, no major alteration in the asymmetric distribution could be observed when probed with phospholipase A2. Since changes in transbilayer mobility of PC and cell morphology occur in HPP cells at lower temperature than in normal red cells, it may be concluded that the enhanced thermal sensitivity of spectrin is the major factor responsible for these changes. Our results therefore support the view that the structural integrity of the skeletal network is essential for stabilization of the lipid bilayer of the red cell membrane.

Sequence comparison of human and murine erythrocyte alpha-spectrin cDNA

The results of hybridization analyses using cDNA probes for mouse and human alpha-spectrin mRNA indicate that a single gene encodes the alpha-subunit of erythrocyte spectrin. Sequencing of the cDNA clones showed that they code for 370 amino acids (aa) covering three repeat domains close to the C terminus of alpha-spectrin. The cloned cDNAs will now permit the isolation of the alpha-spectrin gene and should lead to the characterization of the genetic aspects in human hereditary anemias in which alpha-spectrin has been characterized as the site of the molecular defect.

Molecular and functional changes in spectrin from patients with hereditary pyropoikilocytosis

The structural and functional properties of spectrin from normal and hereditary pyropoikilocytosis (HPP) donors from the two unrelated families were studied. The structural domains of the spectrin molecule were generated by mild tryptic digestion and analyzed by two-dimensional electrophoresis (isoelectric focusing; sodium dodecyl sulfate-polyacrylamide gel electrophoresis). The alpha I-T80 peptide (Mr 80,000) is not detectable in two related HPP donors; instead, two new peptides (Mr 50,000 and 21,000) are generated and have been identified as fragments of the normal alpha I-T80. A third sibling has reduced levels of both the normal alpha I-T80 and the two new peptides. A similar analysis of spectrin from another HPP family indicates that their spectrins contain reduced amounts of the alpha I-T80 and the 50,000 and 21,000 fragments of the alpha I domain. The HPP donor also has other structural variations in the alpha I, alpha II, and alpha III domains. The alpha I-T80 domain of normal spectrin has been shown to be an important site for spectrin oligomerization (J. Morrow and V.T. Marchesi. 1981. J. Cell Biol. 88: 463-468), and in vitro assays indicate that HPP spectrin has an impaired ability to oligomerize. Ghost membranes from HPP donors are also more fragile than membranes from normal erythrocytes when measured by ektacytometry. In both the oligomerization and fragility assays, the degree of impairment is correlated with the amount of normal alpha I-T80 present in the spectrin molecule. We believe that a structural alteration in the alpha I-T80 domain perturbs normal in vivo oligomerization of spectrin, producing a marked decrease in erythrocyte stability.

The spectrin membrane skeleton of normal and abnormal human erythrocytes: a review

The erythrocyte membrane skeleton composed of spectrin, actin, and several other proteins is essential for the maintenance of the erythrocyte shape, reversible deformability, and membrane structural integrity in addition to controlling the lateral mobility of integral membrane proteins. In this review, we shall give an historical development of the current model of the erythrocyte membrane skeleton. We will then describe how the experimental technology developed to study the normal membrane skeleton has paved the way for the recent identification of alterations of skeletal protein interactions in hereditary spherocytosis, hereditary elliptocytosis, and hereditary pyropoikilocytosis. We will conclude with a discussion of some of the more exciting and promising directions for future research that are currently being initiated in this vanguard field of cell biology.

Membrane-active agents and heat-induced erythrocyte fragmentation

Morphological observations of heated erythrocytes were made after preincubation with lysolecithin, diamide, p-chloromercuribenzoate, or N-ethyl maleimide and after ATP-depletion. Diamide (1.0 mM) reduced the critical temperature of fragmentation from 49 degrees C to 47 degrees C, and at higher concentrations the critical temperature was further reduced. The other sulphydryl reacting agents had little or no effect. Drug-induced spherocytes and ATP-depleted cells did not fragment. Membrane-active agents can effect the response of membranes to heat and the effect is dose-dependent.

The molecular basis for membrane - cytoskeleton association in human erythrocytes

Spectrin, the major cytoskeletal protein in erythrocytes, is localized on the inner membrane surface in association with membrane-spanning glycoproteins and with intramembrane particles. The presence of a specific, high-affinity protein binding site for spectrin on the cytoplasmic surface of the membrane has been established by measurement of reassociation of spectrin with spectrin-depleted inside-out vesicles. A 72,000 Mr proteolytic fragment of this attachment protein has been purified, which bound to spectrin in solution and competed for reassociation of spectrin with vesicles. A 215,000 Mr polypeptide has been identified as the precursor of the spectrin-binding fragment. The membrane attachment protein for spectrin was named ankyrin, and has been purified and characterized. Ankyrin has been demonstrated to be tightly associated in detergent extracts of vesicles with band 3, a major membrane-spanning polypeptide, and to bind directly to a proteolytic fragment derived from the cytoplasmic domain of band 3. Ankyrin is thus an example of a protein that directly links a cytoplasmic structural protein to an integral membrane protein. The organization of the erythrocyte membrane has implications for more complex cell types since immunoreactive forms of ankyrin distinct from myosin or filamin have been detected by radioimmunoassay in a variety of cells and tissues. Indirect immunofluorescent staining of cultured cells reveals immunoreactive forms of ankyrin in a cytoplasmic meshwork and in a punctate distribution over nuclei. The staining changes dramatically during mitosis, with concentration of stain at the spindle poles in metaphase and intense staining of the cleavage furrow during cytokinesis.

Calcium ions, drug action and the red cell membrane

Intracellular calcium regulates a number of membrane functions in the erythrocyte, including control of shape, membrane lipid composition and cation permeability. Measurement of total red cell calcium has yielded values between 5 and 15 nmol/ml cells, and these low values in part reflect the absence of Ca2+ -containing organelles. Most intracellular Ca2+ is bound and the low cell ionized Ca2+ concentration (approximately 0.2 microM) is maintained by a combination of low membrane permeability and a powerful Ca2+ -pump. This pump has been identified with a (Ca2+ + Mg2+)-stimulated ATPase, and both Ca2+ transport and ATP splitting are stimulated by calmodulin, a low molecular weight protein which binds Ca2+ avidly and activates many Ca2+ -dependent enzymes. Both high and low affinity kinetics for Ca2+ pumping have been demonstrated, depending on the extent of binding of calmodulin to the pump. A stoichiometry of either 1 or 2 Ca2+ ions pumped per ATP molecule split has been shown, and the value may vary with the level of intracellular Ca2+. Phenothiazines, such as chlorpromazine inhibit the Ca2+ -pump by antagonizing the increment in activity produced by calmodulin. The passive inward leak of Ca2+ into erythrocytes can be quantitated by 45Ca2+ uptake into red cells whose Ca2+ -pump has been inhibited. Estimates of the Ca2+ permeability, based on unidirectional influx, yield values many orders of magnitude lower than for nucleated cells. Influx of Ca2+ into human erythrocytes occurs by a facilitated diffusion process, which can be inhibited by phenothiazines and the cinchona alkaloids. Calcium affects many membrane functions including cation permeability, lipid composition and some cytoskeletal interactions which may determine cell shape. Any rise in intracellular Ca2+ activates a specific K+ channel which normally makes little contribution to K+ fluxes. Kinetic studies of this process demonstrate either high or low affinity Ca2+ -activation of K+ efflux, with low affinity of the channel to Ca2+ being the probable state in vivo. Propranolol is the best known activator of Ca2+ -stimulated K+ efflux, although the mechanism of stimulation is unclear. Like other tissues, red cells possess a Ca2+ -activated phosphoinositol phosphodiesterase. Although it has been suggested that the echinocytic shape change induced by Ca2+ is due to the hydrolysis of polyphosphoinositides, it seems more likely that this shape change results from an effect of Ca2+ on the macromolecular interactions of the cytoskeleton. Abnormal Ca2+ permeability may contribute to red cell destruction in a variety of diseases. For example, in sickle cell anemia a large Ca2+ influx occurs when cells are sickled under deoxy conditions, and moreover, the ability of the Ca2+ -pump to extrude the increment of cell Ca2+ is impaired. Thus, red cell Ca2+ is increased 3-7-fold above normal and this may contribute to the short survival of sickle red cells...

A molecular defect in two families with hemolytic poikilocytic anemia: reduction of high affinity membrane binding sites for ankyrin

Patients from two families with chronic hemolytic anemia have been studied. The erythrocytes are very fragile and appear microcytic with a great variety of shapes. Clinical evaluation failed to identify traditionally recognized causes of hemolysis. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed no significant abnormality of the major polypeptide bands. Erythrocytes spectrin-ankyrin and ankyrin-membrane interactions were analyzed with 125I-labeled spectrin, 125I-labeled ankyrin, and inside-out vesicles. Patients' vesicles bound 125I-spectrin normally. Likewise, patients' spectrin and ankyrin competed normally for the binding sites on control membranes. None of the individual components appeared to have abnormal thermal sensitivity. Ankyrin-stripped, inside-out vesicles prepared from the patients bound less 125I-ankyrin than did vesicles prepared from normals (P less than 0.05 for all corresponding points in the high-affinity region). Scatchard analysis showed the most significant abnormality to be a 50% reduction in the high affinity ankyrin binding sites. Similar experiments were performed with blood from patients with spherocytosis and splenectomized controls, but no abnormalities were detected. The water soluble 43,000-dalton fragments of band 3 (the high-affinity ankyrin binding sites) were prepared from one of the patients and competed normally for 125I-ankyrin binding in solution. This suggests that the primary structural defect is a reduction in the number of high affinity membrane binding sites for ankyrin, and is consistent with an abnormal organization of band 3 in the membrane.

A circular dichroism study of human erythrocyte ghost proteins during exposure to 2450 MHz microwave radiation

The effect of 2450 MHz microwave radiation on the proteins of human erythrocyte ghosts has been investigated using circular dichroism spectroscopy. A specially constructed waveguide inserted into the spectropolarimeter allowed the continuous recording of optical activity before, during and after microwave irradiation. The data indicate that high levels of microwave radiation (600 mW/g, specific absorption rate) induce decreases in alpha-helical conformation that may result from both thermal vibrations and increased strain on the intramolecular hydrogen bonds that maintain secondary structure. The latter effect may result from differential intramolecular interactions with the oscillating electric field. Spectrin (bands 1 and 2) isolated from the ghosts was more sensitive to microwave irradiation than intact ghosts, and spectrin-depleted vesicles were the least sensitive. The data, therefore, indicate that the alpha-helical conformation of spectrin is altered by high levels of microwave radiation.

Altered spectrin dimer-dimer association and instability of erythrocyte membrane skeletons in hereditary pyropoikilocytosis

Hereditary pyropoikilocytosis (HPP) is a hemolytic anemia characterized by microspherocytosis, poikilocytosis, and an unusual thermal sensitivity of erythrocytes. We have investigated the contribution of abnormal membrane skeletal assembly to these abnormal HPP erythrocyte properties. Skeletons prepared from fresh HPP ghosts with Triton X-100 were considerably more fragile than skeletons from control erythrocytes. Spectrin, the major skeleton component, extracted at 0 degrees C from normal erythrocytes, was present primarily as tetramers and high molecular weight complexes. In contrast, spectrin extracted from HPP erythrocytes under identical conditions contained a significant amount of dimers with a concomitant decrease of tetramers. Furthermore, spectrin dimers from HPP erythrocytes differed from normal spectrin dimers in their failure to reassociate into tetramers both in solution and in the membrane. Presumptive HPP carriers (asymptomatic mothers of the two patients) exhibited a mild but reproducible increase of spectrin dimers in 0 degrees C extracts and a defective reassociation of spectrin dimers of tetramers both in solution and in the membrane. We conclude that in HPP, self-association of spectrin dimers into tetramers is defective, which accounts for the instability of membrane skeletons.

Ovalocytic erythrocytes from Melanesians are resistant to invasion by malaria parasites in culture

Ovalocytic erythrocytes from Melanesians in Papua New Guinea have been demonstrated to be resistant to infection by malaria parasites (Plasmodium falciparum) in culture by using a double-label fluorescence assay of merozoite invasion. That merozoites do not bind irreversibly to ovalocytes has been demonstrated by an assay that measures competition between ovalocytes and normocytes. Analysis of behavior on thermal deformation has demonstrated that ovalocytes are more more thermostable than normocytes, suggesting that there is a major difference in cytoskeletal structure. These findings with P. falciparum and epidemiological data demonstrating clinical resistance to P. vivax and P. malariae suggest that the membrane alterations(s) in these ovalocytes affect(s) invasion step(s) common to all three species of malaria parasite.

Tryptic digestion of spectrin in variants of hereditary elliptocytosis

Spectrin, either in the form of unfractionated low ionic strength extracts of erythrocyte membranes or purified by chromatography on Sepharose (CL)4B, was subjected to tryptic digestion at 0 degrees C. Four patients, each with a different variant of hereditary elliptocytosis, were studied. In one patient, whose erythrocytes showed significant fragmentation on heating on 45 degrees C, such preparations generated a remarkably different pattern of polypeptide fragments on tryptic digestion at low ionic strength. In this patient 32P was released at a slower rate on tryptic digestion of labeled band 2, and an unusual 32P-labeled peptide fragment was also generated, in contrast to control preparations in which such a peptide could not be easily distinguished. There was increased susceptibility of this patient's spectrin to tryptic digestion at physiological ionic strength, but the qualitative pattern of polypeptide fragments was normal. Phosphorylation of spectrin by membrane protein kinase was markedly impaired in this patient, whereas phosphorylation of casein ws unimpaired. However, the phosphorylation of spectrin in her intact erythrocytes was normal. Our findings suggest an abnormality of spectrin structure which we postulate is causally related to the predisposition to hemolysis in this patient, but do not distinguish whether this is a primary abnormality or a post-translational modification of the spectrin molecule. The other three patients showed normal tryptic digestion of spectrin.