Water-soluble proteins of the human red cell membrane

Volume regulatory responses of basolateral membrane vesicles from Necturus enterocytes: role of the cytoskeleton

Previous studies from this laboratory have demonstrated that basolateral membrane vesicles isolated from Necturus maculosus small intestinal epithelial cells possess a K(+) channel that is inhibited by ATP. In the present studies, we demonstrate that these vesicles, which are essentially devoid of soluble cytoplasmic contaminants, exhibit volume regulatory responses that parallel those of intact epithelial cells. Thus, suspension of these vesicles in a solution that is hypotonic to the intravesicular solution increases channel activity whereas suspension in a solution that is hypertonic to the intravesicular solution decreases, and may abolish, channel activity. These volume regulatory responses appear to be mediated by the same K(ATP) channel and depend on an intact actin cytoskeletal network. The responses to both hypotonic and hypertonic challenge are abolished by cytochalasin D or by incubating the vesicles under conditions that are known to depolymerize actin. Phalloidin, which is known to stabilize actin filaments, partially prevents the action of cytochalasin D. Thus, the present results indicate that the K(ATP) channel activity of basolateral membrane vesicles from Necturus basolateral membranes respond to hypo- and hypertonic challenge monotonically around an isotonic "set point" and that these responses depend on an intact actin cytoskeleton.

Individual variations of the seven carbohydrate components of human erythrocyte membrane during aging in vivo

The contents of fucose, mannose, galactose, glucose, 2-acetamido-2-deoxy-D-glucose and -D-galactose, and sialic acid, when the results were expressed as nmol per mg of membrane dry-weights, were found to be significantly lower in the membranes of old erythrocytes than in the membranes of young ones. No significant difference was found between young and old membranes when the compositions were expressed as residues per one hundred carbohydrate residues, suggesting that a homogeneous decrease of the carbohydrate moieties may occur during aging in vivo.

Purification of a water-soluble Mg2+-ATPase from human erythrocyte membranes

A water-soluble Mg2+-ATPase previously reported (White, M.D. and Ralston, G.B. (1976) Biochim. Biophys. Acta 436, 567-576) has been purified from human erythrocyte membranes. The purified enzyme has a molecular weight of 575 000; the apparent minimum molecular weight was 100 000, corresponding to a soluble protein of the component 3 region. The Km value for ATP was 1 mM and apparent Km for Mg2+ was 3.6 mM. By means of histochemical activity staining in acrylamide gels it was shown that the purified ATPase preparation could be inhibited by Cd2+ and Zn2+ salts, p-chloromercuribenzoate and N-ethylmaleimide, known inhibitors of membrane endocytosis.

The 'hollow cylinder' protein of erythrocyte membranes

The 'hollow cylinder' protein (Harris, J.R. (1968) Biochim. Biophys. Acta 150, 534-537) has been purified from human erythrocyte membranes. The molecular weight of the native protein, as determined by analytical ultracentrifugation, was found to be 747,000. By means of sodium dodecyl sulphate gel electrophoresis, the purified protein was shown to be composed of three different low molecular weight polypeptides of average molecular weight 25,000. This study provides convincing evidence that the spectrin tetramer is not responsible for the characteristic electron microscopic appearance of the hollow cylinder protein.

Hemoglobin-depleted human erythrocyte ghosts: characterization of morphology and transport functions

A method of preparing hemoglobin-depleted resealed ghosts with an extremely low hemoglobin content is described. The membrane morphology, the crossed immunoelectrophoresis pattern of the membrane proteins, and the transport function of these ghosts have been examined. Electron microscopic examination of the ghosts on hydrophilic as well as hydrophobic grid surfaces revealed a faint filamentous network (spectrin) associated with the membrane. The ghosts were found to have permeabilities towards small polar molecules (water and mannitol) and ions (chloride, sodium, and potassium) which are quantitatively very close to those of intact red cells. It is concluded that white ghosts prepared by the present method are well suited for simultaneous studies of morphology, membrane biochemistry, and membrane transport functions.

Erythrocyte membrane proteins: a modified Gorter-Grendel experiment

The pressure-area isotherm and shear resistance of spectrin-actin monolayers indicate a close-packed structure at about 1.0 m2/mg protein. This surface area is equivalent to a thickness of about two monolayers at the erythrocyte membrane inner face. The maximum elasticity (lowest compressibility) occurs at 0.7 mg2/mg protein, indicating the limit of reversible compression. The mechanical properties of the monolayers approximate those of the intact membrane, suggesting that the structures are similar and that these monolayers may account for many of the in vivo properties.

Phospholipase A2 from sheep erythrocyte membranes. Ca2+ dependence and localization

The calcium dependence and the time course of phosphatidylethanolamine and phosphatidylcholine degradation by sheep erythrocyte membrane suspensions in presence of Triton X-100 were investigated. One enzyme with phospholipase A2 specificity was found to be responsible for both phosphatidyl-ethanolamine and phosphatidylcholine degradation. The localization of this enzyme in the membrane of the sheep erythrocyte was investigated by proteolytic treatment of sealed erythrocyte ghosts from the outside and of ghosts which had both sides of the membrane exposed to chymotrypsin. The inability of sealed ghosts to take up chymotrypsin was followed by flux measurements of [14C]dextran carboxyl previously trapped in the ghosts. No efflux of the marker was found during the proteolytic treatment. By comparing the residual phospholipase activities in the membranes from both ghost preparations, we concluded that the phospholipase is oriented to the exterior of the sheep erythrocyte.

Localization and role of calcium in the erythrocyte coat: effects of enzymes and storage

The effects of various treatments on erythrocyte shape, surface, cell coat and calcium binding sites have been investigated by means of high voltage electron microscopy (HVM), scanning electron microscopy (SEM) and conventional electron microscopy (TEM). Papain caused the formation of small blisters within the cellular surface as well as crenation and 'budding' of the erythrocytes. After neuraminidase treatment, long filaments were observed to radiate from the surface of the erythrocyte. The other enzymes investigated, RNA'se DNA'se, phospholipase, protease and trypsin, produced no demonstrable effect on the cellular structure, nor (with the possible exception of trypsin) on the cell coat as seen by subsequent staining with ruthenium red. Putative calcium binding sites on and in the erythrocyte membrane were demonstrated. Following incubation with radioactive calcium, activity was found in the erythrocyte membranes. Calcium binding could be reduced by prior treatment of the erythrocyte with EDTA, neuraminidase, and to a lesser extent, by papain and trypsin. Other enzymes had no demonstrable effect. Stored erythrocytes showed a progressive diminution in calcium binding over a period of up to 4 weeks.

The effect of synthetic polymers on the electrical and permeability properties of lipid membranes

1. The effect of two series of hydrophilic and hydrophobic polymers on the stability, conductivity and permeability towards water and leucine of black lipid membranes and liposomes is reported. 2. The changes in properties of these membrane preparations is related to bulk phase viscosity and dielectric measurements together with monolayer studies. 3. The hydrophobic polymers dramatically increase membrane stability, had no effect on conductivity, but increased the permeability coefficient of leucine. 4. The hydrophilic polymers produced minor, but significant changes to membrane properties. 5. It is concluded that not only basic polymers but also neutral and acidic macromolecules can interact strongly with lipid membranes.

Hypertonic cryohemolysis: ionophore and pH effects

Human erythrocytes suspended at 37 degrees C in hypertonic solution of either electrolytes or nonelectrolytes undergo hemolysis when the temperature is lowered toward 0 degrees C (Green, F.A., Jung, C.Y. 1977 J. Membrane Biol. 33:249). In the present studies this hypertonic cryohemolysis was profoundly affected by the pH of incubation, and was completely abolished at ph 5. In hypertonic NaCl, there was an apparent pH optimum at 6--6.5. In hypertonic sucrose, on the other hand, hemolysis increased progressively with increasing pH between 6 and 9. Amphotericin B inhibited hypertonic cryohemolysis in NaCl or KCl solution. No inhibiting effect of amphotericin B was observed when hypertonicity was due to sodium sulfate or sucrose. Valinomycin also inhibited hypertonic cryohemolysis in KCl, but did not affect the process in NaCl or sucrose solution. SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate) and phloretin interfered with this valinomycin effect, whereas phlorizin did not. These results indicate that dissipation of an osmotic gradient across membranes may be responsible for the inhibition of the hemolysis by these inophores. Iso-osmotic cell shrinkage induced by valinomycin in 150 mM NaCl solution did not result in cryohemolysis.

Phospholipid composition of human erythrocyte spectrin

Human erythrocyte spectrin, which has been extracted at low ionic strength and precipitated at pH 5.1, contains 0.025 mumoles phospholipid/mg protein. The composition of the spectrin-phospholipids differs from that of the erythrocyte membrane. A remarkable similarity was found between the composition of the "available" phospholipids of the inner leaflet of the membrane bilayer and the spectrin-associated phospholipids. Rebinding studies with 125I-labeled spectrin show that the labeled spectrin binds preferentially to the cytoplasmic side of the membrane and that this binding is influenced by protein perturbations.

Ca binding to the human red cell membrane: characterization of membrane preparations and binding sites

Inside out and right side out vesicles were used to study the sidedness of Ca binding to the human red cell membrane. It was shown that these vesicles exhibited only a limited permeability to Ca, enabling the independent characterization of Ca binding to the extracellular and cytoplasmic membrane surfaces...

A water-soluble Mg2+-ATPase from erythrocyte membranes

A ouabain-insensitive ATPase activity associated with the water-soluble proteins of the human and bovine erythrocyte membrane is demonstrated by means of activity-staining in polyacrylamide gels. The ATPase activity from both sources had an absolute requirement for Mg2+, activity becoming easily detectable at 0.2 mM Mg2+. At low Mg2+ concentrations added Ca2+ appeared to decrease the intensity of the ATPase stain. The activity is unaffected by monovalent cations, does not hydrolyse p-nitrophenyl phosphate and is not inhibited by 2 : 4 dinitrophenol. The ATPase has an apparent molecular weight of approximately 100 000 as determined by electrophoresis in acrylamide gels containing dodecyl sulphate.

Unique properties of the camel erythrocyte membrane, II. Organization of membrane proteins

Camel erythrocyte membranes are distinguished by some unique properties of stability and composition. Notable is their abundance in proteins (protein:lipid ratio of 3:1). Membrane proteins of camel erythrocytes were compared with those of human eruthrocytes, which have been intensively investigated. Proteins were extracted with various aqueous media (EDTA, alkaline or high ionic strength) and with ionic and non-ionic detergents and were analyzed by gel electrophoresis. In membranes of camel erythrocytes, the peripheral proteins constitute, proportionally, a much smaller fraction of total proteins than in the human erythrocyte, while their distribution is identical per unit of surface area. The camel erythrocyte membrane is particularly rich in integral proteins and in intramembranous particles. The proteins in this membrane are more closely organized than in the human system, as revealed by crosslinking and freeze-etching studies. It is proposed that protein-protein interaction of integral proteins, presumably constituting an "integral skeleton", is a dominant structural feature stabilizing the camel erythrocyte membrane.

Effects of pH during recombination of human erythrocyte membrane apoprotein and lipid

The recombinates from human red cell membrane proteins and lipids resulting from dialysis of the components in 2-chloroethanol against aqueous buffers from pH2-12 have been studied by density gradient centrifugation, polyacrylamide gel electrophoresis and freeze-fracture electron microscopy. Between pH 4 and 10 most of the proteins were found in the recombinates whereas below pH 4 and above pH 10 only part of them were recovered in the lipoprotein band after density gradient centrifugation. At low pH, increasing incorporation of the "major glycoprotein" into the recombinates was detected by gel electrophoresis and in parallel increasing amounts of particles were found in the freeze-fracture membrane faces. The necessity of working at low pH values from pH 2-4, however, and a critical evaluation of all the data presently available leads to the conclusion that the 2-choloroethanol technique is not adequate for recombination studies tending to membrane reconsitution.

Intramembrane particle aggregation in erythrocyte ghosts. II. The influence of spectrin aggregation

Physicochemical properties of mixtures of spectrin and actin extracted from human erythrocyte ghosts have been correlated with ultrastructural changes observed in freeze-fractured erythrocyte membranes. (1) Extracted mixtures of spectrin and actin have a very low solubility (less than 30 mug/ml) near their isoelectric point, pH 4.8. These mixtures are also precipitated by low concentrations of Ca2+, Mg2+, polylysine or basic proteins. (2) All conditions which precipitate extracts of spectrin and actin also induce aggregation of the intramembrane particles in spectrin-depleted erythrocyte ghosts. Precipitation of the residual spectrin molecules into small patches on the cytoplasmic surface of the ghost membrane is thought to be the cause of particle aggregations, implying an association between the spectrin molecules and the intramembrane particles. (3) When fresh ghosts are exposed to conditions which precipitate extracts of spectrin and actin, only limited particle aggregation occurs. Instead, the contraction of the intact spectrin meshwork induced by the precipitation conditions compresses the lipid bilayer of the membrane, causing it to bleb off particle-free, protein-free vesicles. (4) The absence of protein in these lipid vesicles implies that all the proteins of the erythrocyte membrane are immobilized by association with either the spectrin meshwork or the intramembrane particles.

Two-dimensional polyacrylamide-gel electrophoresis of the proteins and glycoproteins of the human erythrocyte membrane

A two-dimensional polyacrylamide gel electrophoresis technique has been developed, improving the analytical separation of some proteins and glycoproteins of the human erythrocyte membrane. Freshly prepared membranes are totally solubilized, subjected to dodecylsulfate--polyacrylamide gel electrophoresis in the first dimension, followed by electrophoresis in the second dimension, using a detergent-free polyacrylamide gradient gel. By this method the proteins of the human erythrocyte membrane could be resolved into a two-dimensional pattern, which has been shown to be highly reproducible with respect to various blood-groups and within one blood-group from specimen to specimen. The method enables especially the investigation of the hydrophobic and very likely integrated membrane proteins and glycoproteins. Thus, band III[Fairbanks, G., Steck, Th. & Wallach, D. F. H., Biochemistry, 10, 2606--2617 (1971)] could be shown to consist of five proteins, one of them being the major glycoprotein of the human erythrocyte membrand. The two spectrin bands differed considerably in their two-dimensional patterns. The value of the given method for the investigation of membrane defects, which may be linked with various diseases of human erythrocytes, could be demonstrated in the case of two patients suffering from congenital dyserythropoetic anaemia.

The kinetics of resealing of washed erythrocyte ghosts

The kinetics of resealing, defined as the recovery of impermeability to macromolecules, of well-washed human erythrocyte ghosts has been determined. The resealing process is first-order at temperatures above 20-25 degrees C in isotonic salt, with rate constants ranging from 0.01-0.15 min-1. Below 20 degrees C, resealing occurs, but a long lag period is observed. Other erythrocyte membrane properties suggest a transition at about 20 degrees C, and it is possible that resealing rates are a measure of membrane fluidity. A temperature-induced reduction of resealed ghost volume was also observed. The effect of ionic strength on resealing parameters was determined. Low ionic strength buffers prevent resealing, which is also consistent with resealing as a lipid-related event. The effect of microtubule disrupting drugs and changes in the method of preparing ghosts are also described.

A comparison of intact human red blood cells and resealed and leaky ghosts with respect to their interactions with surface labelling agents and proteolytic enzymes

Resealed ghosts and intact red blood cells were directly compared with respect to their interactions with surface proteins by 4.4'-diisothiocyano-2,2'-stilbene disulfonic acid (DIDS) and by pyridoxal phosphate-borohydride (as seen after sodium dodecylsulfate/acrylamide gel electrophoresis) was substantially the same in cells and resealed ghosts under conditions in which a relatively small change would be apparent. In each membrane system, DIDS labels a protein component of apparent molecular weight 95 000 and pyridoxal phosphate labels the same protein plus three glucoprotein components. The sensitivity of surface proteins and of DIDS and pyridoxal phosphate-labelled sites to pronase was also similar in the cells and resealed ghosts. The glycoproteins were digested, in each case, and the 95 000 (molecular weight) protein was largely split into two proteins of apparent molecular weights 65 000 and 35 000, with both portions containing DIDS and pyridoxal phosphate in the presence of hemoglobin was similar to the labelling of intact cells, provided that the pyridoxal phosphate was present on both the outside and inside of the cells. Virtually all of the major protein components visible by staining on acrylamide gels were labelled. It is concluded that none of the probes could detect any substantial differences in reactivity of proteins of the outer surface of the membrane protein conformation or arrangement occur as a consequence of lysis and resealing of ghosts, that are detectable by the reported procedures.

Interaction of Clostridium perfringens theta-haemolysin, a contaminant of commercial phospholipase C, with erythrocyte ghost membranes and lipid dispersions. A morphological study

Commercially available preparations of phospholipase C from Clostridium perfringens are commonly contaminated with theta haemolysin, one of a group of bacterial haemolysins called oxygen labile (O-labile) haemolysins. Treatment of erythrocyte ghosts and a mixed lipid dispersion containing cholesterol with commercially available phospholipase C in the absence of Ca-2+ and the presence of phosphate buffer and/or EDTA resulted in the formation and release of ring or arc-shaped structures. Highly purified phospholipase C, free of theta-haemolysin, produced no changes in the morphology of erythrocyte ghosts or lipid dispersions in the presence of phosphate or EDTA, but caused the formation of typical diglyceride droplets in the presence of Ca-2+ in the absence of these inhibitors. Ring structures, identical to those caused by commercial phospholipase C, were formed on addition of highly purified theta-haemolysin to erythrocyte ghost membranes, lipid dispersions containing cholesterol and cholesterol dispersions, but not on treatment of membranes from Micrococcus lysodeikticus. Heat-inactivated O-haemolysin (60 degrees C for 10 min) produced no such effects. The dimensions of rings and arcs displayed heterogeneity. The outside diameters in various preparations varied from approx. 27-58 nm with border thickness of 4.1-7.8 nm.

The N-terminal heterogeneity of edta-extractable erythrocyte membrane proteins

N-terminal analysis of the proteins extracted from ox (Bos taurus) erythrocyte membranes by dilute EDTA is used as a means of estimating the heterogeneity of the protein fractions. Dinitrophenylation and dansylation reveal up to 8 different N-terminal amino acids in fractions with electrophoresis after dodecylsulphate treatment shows as having far fewer polypeptide chains. These fractions are prepared by gel electrophoresis in the presence and absense of detergent. Molecular weight estimation by the Ferguson procedure of the components revealed in the EDTA extract by electrophoresis in the absence of detergent confirms the large size concluded from electrophoresis with dodecylsulphate. The N-terminal analyses indicate that the high molecular weight of the complexes, both in the presence and absence of detergent, is more probably due to their being complexes of several polypeptides than exceptionally long single polypeptide chains.

Actin-activated ATPase from human erythrocytes

A fibrillar protein complex, possessing ouabain-insensitive Ca2+-ATPase activity was isolated from human erythrocyte membranes by using a low ionic strength extraction procedure. Mg2+-ATPase activity was revealed upon addition of rabbit skeletal muscle actin, thus demonstrating the presence of a myosin-like protein in the crude extract of the erythrocyte membrane. Upon sodium dodecylsulfate gel electrophoresis, the extract showed mainly the doublet of subunit molecular weight bands of 230 000 and 210 000, and more than 10 faster moving bands. Gel filtration of the erythrocyte membrane extract on Sepharose 4B furnished 4 fractions. Fraction I, containing the doublet and 80 000, 60 000 and 46 000 subunit molecular weight bands was 5-fold purified with respect to Ca2+-ATPase activity, but was devoid of actin-activated Mg2+-ATPase activity. Fraction II, containing only the doublet, was devoid of Ca2+ and actin-activated Mg2+-ATPase activity. The 210 000 subunit molecular weight protein could be phosphorylated in the presence of Mg2+ in the crude extract and Fraction I but not in Fraction II.

Calcium and magnesium ATPases of the spectrin fraction of human erythrocytes

Using a rapid method of preparation, spectrin has been isolated from human erythrocytes and its ATPase activity investigated. The ATPase activity with calcium has two distinct components, one with optimal activity when calcium and ATP are of equal concentration (low-Ca-ATPase) and another which is activated above 1 mM CaCl2 and is maximal at 100 mM CaCl2. There is also a Mg-ATPase with maximal activity at 10 mM MgCl2. The high-Ca-ATPase of spectrin, but not the low-Ca-ATPase, is inhibited by magnesium, while the Mg-ATPase is inhibited by Ca in excess of ATP. None of these activities exhibits the calcium-stimulated magnesium-dependent activity characteristic of the red cell calcium pump.