Mammalian Erythrocyte Membranes Research Articles

Correlation between sphingomyelin and the membrane stability of mammalian erythrocytes.

Lipid compositions of mammalian erythrocyte membranes are different among species. Therefore, the information on hemolysis from mammalian erythrocytes is useful to understand membrane properties of human erythrocytes. In this work, pressure-induced hemolysis and hypotonic one were examined using erythrocytes of human, sheep, cow, cat, dog, pig, horse, rat, and mouse. Pressure-induced hemolysis was suppressed by membrane sphingomyelin, whereas hypotonic hemolysis decreased upon increment of cell diameter. Mass spectra of erythrocyte membrane lipids demonstrated that sphingomyelin with an acyl chain 24:1 was associated with the suppression of pressure-induced hemolysis. In cow erythrocytes, pressure-induced hemolysis was greatly suppressed and the detachment of cytoskeletal proteins from the membrane under hypotonic conditions was also inhibited. Taken together, these results suggest that sphingomyelin with 24:1 fatty acid plays an important role in the stability of the erythrocyte membrane, perhaps via cholesterol.

Вплив мембранотропних речовин на чутливість еритроцитів ссавців до дії постгіпертонічного шоку

The effect of cationic trifluoperazine (TFP) and nonionic decyl-β,D-glucopyranoside (DGP) on the sensitivity of human, rabbit and rat erythrocytes to the action of posthypertonic shock (PHS) at 0 °C was studied in this research. Trifluoperazine shows a high antihemolytic activity under conditions of PHS of human and animal erythrocytes at slight differences of values of effective concentrations. The value of antihemolytic activity of TFP for human and rabbit erythrocytes is ~ 60 %, and for rat cells the efficiency of this compound is approximately 1.4 times higher. The values of antihemolytic activity of DGP under PHS conditions of human and rat erythrocytes are comparable and amounts to 62 and 66 %, respectively. Significant differen­ces of this parameter (72 %) were found for rabbit cells compared with human erythrocytes. It was found that the size of plateau (the range of concentrations of amphiphilic compounds within the minimum level of erythrocyte hemolysis was observed) cationic TFP and nonionic DGP are significantly different. Thus, TFP has a narrow plateau (100–200 μmol/L), while DGP has a rather wide one (400–1600 μmol/L). In addition, a shift of the plateau concentrations of DGP to the region of higher values compared with TFP is observed, which is probably due to the fact that the value of the critical micelle concentration DGP is higher than TFP. Moreover, a shift of plateau concentrations of DGP to the region of higher values compared with TFP is observed, that is probably due to the fact that the value of the critical micelle concentration DGP is higher than TFP one. It was established that under PHS conditions of human erythrocyte, both compounds (TFP and DGP) show a commensurate antihemolytic activity. At the same time, for rabbit cells, DGP is more effective compared with TFP, and for rat erythrocytes, on the contrary, the efficiency of TFP is higher than DGP. This may be due to differences in the phospholipid composition of mammalian erythrocyte membranes. The results suggest that under PHS conditions the efficacy of membrane-tropic compounds is most likely due to their ability to incorporate into membrane to the defect formation areas, and thus significantly increase the critical hemolytic volume of cells, as a result, prevent their destruction.

The role of interspecies differences in the ratio of choline-containing phospholipid fractions of rodent erythrocytes in response of these cells to the effect of membranotropic compounds

In in vitro experiments, interspecies differences were revealed in the erythrocyte responses in varied rodent species—laboratory mice (Mus musculus L.), tundra voles (Microtus oeconomus Pall.) and bank voles (Myodes glareolus Pall.)—to the effect of chemical agents able to interact with membrane lipids and disrupt the membrane structure (detergent Triton X-100, oxidative stress inductor AAPH, antioxidant ionol or BHT, uranyl ion). It was hypothesized that these differences are due to physicochemical peculiarities of the erythrocyte membrane structure, specifically, the ratio of choline-containing fractions of phospholipids (phosphatidylcholine and sphingomyelin). The use of blood erythrocytes as an in vitro experimental model to study the mechanisms of toxicity as well as antioxidant and membrane-protective properties of compounds of different nature was shown to imply the choice of an adequate source of erythrocytes in view of considerable speciesdependent structural specificity of the lipid component of mammalian erythrocyte membranes.

COMPARATIVE STUDY OF MECHANICAL STRESS EFFECT ON HUMAN AND ANIMAL ERYTHROCYTES

Sensitivity of human and animal (bovine, rat, rabbit, equine) erythrocytes to the effect of mechanical stress has been studied. Mechanical stress effect was demonstrated to result in a time-dependent (5-60 min) release of potassium cations out of mammalian erythrocytes and a partial hemolytic cell damage. Herewith the release levels of potassium ions and hemolysis did not coincide for erythrocytes of all the mammals except rabbit ones. The most sensitive to mechanical stress (60 min) by the parameters of hemolytic damage and potassium ion release were rat (32%) and bovine (66%) erythrocytes respectively, the lowest sensitive by both parameters were rabbit ones (about 20%). Implemented correlation analysis has demonstrated a statistically significant negative relation between the values of mechanical hemolysis of mammalian erythrocytes and surface-volumetric ratio of cells (rs = -0.900, P = 0.037). A feasible relationship between the content of phosphatidylethanolamine in mammalian erythrocyte membranes and the level of potassium cation loss under mechanical stress effect is under discussion.

Sialoglycoproteins of Mammalian Erythrocyte Membranes: A Comparative Study

The presence of sialoglycoproteins (SGPs) in the membranes from goat (Capra aegagrus hircus), buffalo (Bubalus bubalis bubalis) and pig (Sus scrofa domestica) erythrocytes was investigated by partial purification with a chloroform-methanol extraction method followed by Sodium dodecyl sulphate - Polyacrylamide gel electrophoresis in comparison to human (Homo sapiens) erythrocytes. The results show that mammalian erythrocytes possess clear differences in the SGPs numbers and molecular weights although all animals studied in this experiment are from the same class i.e. mammalia. The SGPs number in human, goat, buffalo and pig are four (PAS-1 to PAS-4), ten (PAS-GI to PAS-GX), seven (PAS-BI to PAS-BVII) and four (PAS-PI to PAS-IV) respectively as indicated by staining the polyacrylamide gel with sialoglycoprotein-specific Periodic acid-Schiff's (PAS) stain. The new SGPs could be observed only after the partial purification of membrane fractions named as PAS-HI with molecular weight (Mr) 190 kDa and PAS-HII 150 kDa in human, PAS-BIA in buffalo and PAS-PIA and PAS-PIVA in pig. The gels were also stained with Coomassie brilliant blue (CBB) and Silver stain to check the contamination of other membrane proteins in the purified fractions. The quantitative distribution of SGPs was also determined by densitometry. Present study indicates that there are some basic differences in mammalian erythrocyte membrane SGPs, especially with respect to their number and molecular weights indicating major structural variations.

Characterization of glycolytic enzyme interactions with murine erythrocyte membranes in wild-type and membrane protein knockout mice

Previous research has shown that glycolytic enzymes (GEs) exist as multienzyme complexes on the inner surface of human erythrocyte membranes. Because GE binding sites have been mapped to sequences on the membrane protein, band 3, that are not conserved in other mammalian homologs, the question arose whether GEs can organize into complexes on other mammalian erythrocyte membranes. To address this, murine erythrocytes were stained with antibodies to glyceraldehyde-3-phosphate dehydrogenase, aldolase, phosphofructokinase, lactate dehydrogenase, and pyruvate kinase and analyzed by confocal microscopy. GEs were found to localize to the membrane in oxygenated erythrocytes but redistributed to the cytoplasm upon deoxygenation, as seen in human erythrocytes. To identify membrane proteins involved in GE assembly, erythrocytes from mice lacking each of the major erythrocyte membrane proteins were examined for GE localization. GEs from band 3 knockout mice were not membrane associated but distributed throughout the cytoplasm, regardless of erythrocyte oxygenation state. In contrast, erythrocytes from mice lacking alpha-spectrin, ankyrin, protein 4.2, protein 4.1, beta-adducin, or dematin headpiece exhibited GEs bound to the membrane. These data suggest that oxygenation-dependent assembly of GEs on the membrane could be a general phenomenon of mammalian erythrocytes and that stability of these interactions depends primarily on band 3.

Antibodies to βIΣ2 spectrin identify in-homogeneities in the erythrocyte membrane skeleton

The cortical cytoskeleton of the mammalian red cell, composed of spectrin, actin, protein 4.1, adducin, and protein 4.9, is generally regarded as a homogeneous structure that maintains the integrity of the membrane and the lateral disposition of integral membrane proteins. The major component of this structure is a hetero-oligomer of αI and βIΣ1 spectrin. In other tissues, most notably muscle and brain, a transcript of the βI spectrin gene is generated by alternative exon utilization, yielding a protein that has the COOH-terminal 19 residues of βIΣ1 spectrin replaced by 210 novel residues to generate βIΣ2 spectrin. This new transcript contains a pleckstrin homology (PH) domain and may even exist under some conditions in a homopolymeric form. Using antibodies specific for the COOH-terminal domains of either βIΣ1 or βIΣ2 spectrin, we find that contrary to previous understandings, mature human erythrocytes contain a subpopulation of spectrin that is immunoreactive with antibodies to the βIΣ2 isoform, and that this spectrin is distributed into distinct plasma membrane patches. These results suggest that the native mammalian erythrocyte membrane skeleton, rather than being homogeneous, contains discrete submicron-scale microdomains that differ in both their composition and dispersion across the cell surface. The precise nature and role of these putative microdomains is under active investigation.

Viscoelasticity: Fractal parameters studied on mammalian erythrocytes under shear stress

In this work, experimental determinations are carried out using a home-made device called an erythrodeformeter, which has been developed and constructed for rheological measurements on red blood cells subjected to definite fluid shear stress. A numerical method formulated on the basis of the fractal approximation for ordinary and fractionary Brownian motion1 is proposed to evaluate the viscoelastic behavior of mammalian erythrocyte membranes. The diffraction pattern, which is circular when the mammalian erythrocyte membranes are at rest, becomes elliptical when the cells undergo shear stress. Photometric readings of light intensity variation along the major axis of the elliptical diffraction pattern are recorded during the creep and recovery process. These data series are used to calculate, fractal rheological parameters of self-affine Brownian motion on the erythrocytes, averaged over several millions of cells. Three different parameters over the time dependent process could be obtained, which are: correlation coefficient , correlation integral, andK2-entropy, and very different results were obtained.

Effect of phospholipase C, trypsin and neuraminidase on binding of bilirubin to mammalian erythrocyte membranes

Binding of bilirubin to erythrocyte membranes of human, buffalo, sheep and goat was studied after phospholipase C, trypsin and neuraminidase treatment. Phospholipase C and trypsin treatment of membranes greatly enhanced the bilirubin binding in all mammalian species, whereas, neuraminidase treatment resulted into a small increase in the membrane-bound bilirubin. Human erythrocyte membranes bound the highest amount of bilirubin, whereas buffalo, sheep and goat erythrocyte membranes showed different mode of bilirubin binding. The order of bilirubin binding to unmodified as well as neuraminidase-treated erythrocyte membranes was: human>sheep>buffalo>goat; the order was: human>buffalo>sheep>goat; in phospholipase C- and trypsin-treated erythrocyte membranes. These binding results indicate that membrane phospholipids are directly involved in the interaction of bilirubin with the membranes as the differences observed in the membrane-bound bilirubin among mammalian species were directly correlated with the sum of choline phospholipids, especially phosphatidylcholine and sphingomyelin content of the erythrocyte membranes. The negatively charged phosphate moiety of phospholipids of the membranes appears to inhibit a large amount of bilirubin binding to the membrane as its removal by phospholipase C greatly enhanced the binding. Furthermore, membrane proteins and carbohydrate also seem to play a significant regulatory function on the binding as their degradation and/or removal in the form of glycopeptides by trypsin expose a large number of bilirubin binding sites.

Solubilization, reconstitution and molecular properties of the triiodothyronine transport protein from rat erythrocyte membranes.

Triiodothyronine (T3) transport through the mammalian erythrocyte membrane is mediated by a transport system related to the aromatic amino acid transport system T. The T3-binding component of this transport system could be photolabeled with [125I]T3 as a 52-kD protein, and subsequently solubilized with non-ionic detergents. Upon purification by ion-exchange chromatography, the photolabeled 52-kD protein solubilized with octylglucoside (OG) resolved into several peaks, suggesting charge heterogeneity of labeled proteins. The saturable [125I]T3 binding to rat erythrocyte membranes was completely inhibited by non-ionic detergents at concentrations about 20 times lower than those that solubilized membrane. Therefore, detergent-free proteoliposomes were generated from the detergent-soluble extracts by treatment with a polystyrene adsorbent. Proteoliposomes prepared from OG-soluble extract contained the highest specific activity of T3 binding. The Kd of the T3 binding sites (4.5 nmol/l) and the competitive inhibition constant of tryptophan (120 mumol/l) were similar to those for native membranes. The photolabeling of the 52-kD protein in these proteoliposomes was prevented by tryptophan and T4, but not by leucine or the D-isomer of T3, corresponding to the transport specificity of system T. The 52-kD protein solubilized with OG from native membranes was partially purified by ion-exchange chromatography. The 52-kD protein was detected by photoaffinity labeling in the purified fraction only after addition of erythrocyte membrane phospholipids to generate proteoliposomes. This indicates that the association of 52-kD protein with phospholipids is critical for T3 binding.

The gene encoding the erythrocyte membrane skeleton protein dematin ( Epb4.9) maps to mouse chromosome 14

The mammalian erythrocyte membrane skeleton primarily consists of spectrin, actin, protein 4.1 (numerals refer to electrophoretic mobility on SDS-PAGE gels), and dematin (protein 4.9). Although the functional interactions of spectrin, actin, and protein 4.1 have been extensively characterized, virtually nothing is known about the physiological role of dematin. Spectrin is present as elongated heterodimers of {alpha}- and {beta}-subunits arranged in a two-dimensional array just beneath the plasma membrane. The mechanism by which the {open_quotes}head{close_quotes} region of the spectrin dimer binds to the plasma membrane via ankyrin and band 3 is well established. However, the mechanism by which the {open_quotes}tail{close_quotes} end of spectrin is anchored to the plasma membrane is not completely understood. The region containing the spectrin tails is called the junctional complex. Protein 4.1, actin, adducin, and dematin have been directly visualized as components of junctional complexes. Other components of junctional complexes include tropomyosin, tropomodulin, and p55. Protein 4.1 acts as an adaptor protein, linking spectrin-actin complexes to the plasma membrane. Dematin binds actin and therefore also may function as an adaptor protein in mature erythrocytes. Dematin also displays phosphorylation-dependent actin bundling activity. Since actin bundles appear to be absent from mature erythrocytes, this property may be most relevantmore » during erythropoiesis and in nonerythroid cells. The cDNA sequence of human dematin shows significant identity with the {open_quotes}headpiece{close_quotes} of villin, an actin bundling protein of brush border cytoskeleton. Unlike villin, dematin is a widely distributed protein and may substitute for villin to regulate actin bundling events by a phosphorylation-dependent mechanism. 18 refs., 1 fig.« less

Delivery of ion pumps from exogenous membrane-rich sources into mammalian red blood cells.

Using polyethylene glycol-mediated fusion of ATP-ase-enriched (native) microsomes with red blood cells, we have delivered sarcoplasmic reticulum (SR) Ca-ATPase and kidney Na,K-ATPase into the mammalian erythrocyte membrane. Experiments involving delivery of the SR Ca-ATPase into human red cells were first carried out to assess the feasibility of the fusion protocol. Whereas there was little detectable 45Ca2+ uptake into control cells in either the absence or presence of extracellular ATP, a marked time-dependent uptake of 45Ca2+ was observed in the presence of ATP in cells fused with SR Ca-ATPase. Comparison of the kinetics of uptake into microsome-fused cells versus native SR vesicles supports the conclusion of true delivery of pumps into the red cell membrane. Thus, the time to reach steady state was more than two orders of magnitude longer in the (large) cells versus the native SR vesicles. Na,K-ATPase from dog and rat kidney microsomes were fused with red cells of humans, sheep, and dogs. Using dog kidney microsomes fused with dog red cells which are practically devoid of Na,K-ATPase, functional incorporation of sodium pumps was evidenced in ouabain-sensitive Rb+ uptake and Na+ efflux energized by intracellular ATP, as well as in ATP-stimulated Na+ influx and Rb+ efflux from inside-out membrane vesicles prepared from the fusion-treated cells. From analysis of the biphasic kinetics of ouabain-sensitive Na+ efflux under conditions of limited intracellular Na+ concentration, it is concluded that the kidney pumps are incorporated into a relatively small fraction (approximately 15%) of the red cells. This system provides a uniquely useful system for studying the behavior of native sodium pumps in a compartment (red cell) of small surface/volume ratio. The newly incorporated native kidney pumps, while of the same isoform as the endogenous red cell pump, behave differently from the endogenous red cell sodium pump with respect to their very low "uncoupled" Na+/O flux activity.

Susceptibility of salmonid erythrocytes to lysis by bacterial lipopolysaccharides

Abstract. Bacterial lipopolysaccharide (LPS) is known to have binding affinity for mammalian erythrocyte membranes but does not cause haemolysis. In this study, LPS from eight different bacterial species all possessed haemolytic activity for salmonid erythrocytes. There were some differences in haemolytic activity among the different bacterial LPS after 2 h incubation. Lytic titres continued to increase with time for some LPS species reaching extremely high litres after 20 h incubation for the Salmonella minnesota LPS. The LPS extracted by the hot‐phenol method from extracellular products (ECP) of Aeromonas salmonicida was more haemolytic than that extracted from the bacterial cell walls. Separated lipid A‐ and O‐antigen fractions of A. salmonicida LPS had a similar low haemolytic activity. When A. salmonicida LPS, lipid A‐ and O‐antigen were pre‐incubated with bovine serum albumin, only LPS extracted from ECP retained any haemolytic activity. The LPS types used in this study were not haemolytic for rabbit erythrocytes.

Beta spectrin in human skeletal muscle. Tissue-specific differential processing of 3' beta spectrin pre-mRNA generates a beta spectrin isoform with a unique carboxyl terminus

Spectrin, an important component of the mammalian erythrocyte membrane skeleton, is a heterodimeric protein with alpha and beta subunits of 280 and 246 kDa, respectively. Spectrin-like proteins have also been demonstrated in a wide variety of nonerythroid cells. To examine the hypothesis that nonerythroid beta spectrins may be encoded by the "erythroid" beta spectrin gene, we have isolated cDNA clones from a human fetal skeletal muscle library by hybridization to a previously described red cell beta spectrin cDNA. Detailed comparison of muscle and erythroid beta spectrin cDNAs has revealed sequence identity over the majority of their lengths, confirming that they are the product of the same gene. However, there is a sharp divergence in sequence at their 3' ends. A consequence of this divergence is the replacement of the carboxyl terminus of erythroid beta spectrin with a different, longer carboxyl-terminal domain in skeletal muscle. We hypothesize that tissue-specific differential polyadenylation leads to the selective activation of a donor splice site within the beta spectrin coding sequence, splicing downstream nonerythroid exons into the mature muscle beta spectrin mRNA. We predict that replacement, in nonerythroid cells, of the beta spectrin carboxyl terminus, known to participate in spectrin self-association and phosphorylation, has significant functional consequences. These data may explain previously reported nonerythroid beta spectrin isoforms that resemble red cell beta spectrin by immunochemical analysis.

Changes in erythroid membrane proteins during erythropoietin-mediated terminal differentiation.

Membrane and membrane skeleton proteins were examined in erythroid progenitor cells during terminal differentiation. The employed model system of erythroid differentiation was that in which proerythroblasts from mice infected with the anemia-inducing strain of Friend virus differentiate in vitro in response to erythropoietin (EP). With this system, developmentally homogeneous populations of cells can be examined morphologically and biochemically as they progress from proerythroblasts through enucleated reticulocytes. alpha and beta spectrins, the major proteins of the erythrocyte membrane skeleton, are synthesized in the erythroblasts both before and after EP exposure. At all times large portions of the newly synthesized spectrins exist in and are turned over in the cytoplasm. The remaining newly synthesized spectrin is found in a cellular fraction containing total membranes. Pulse-chase experiments show that little of the cytoplasmic spectrins become membrane associated, but that the proportion of newly synthesized spectrin which is membrane associated increases as maturation proceeds. A membrane fraction enriched in plasma membranes has significant differences in the stoichiometry of spectrin accumulation as compared to total cellular membranes. Synthesis of band 3 protein, the anion transporter, is induced only after EP addition to the erythroblasts. All of the newly synthesized band 3 is membrane associated. A two-dimensional gel survey was conducted of newly synthesized proteins in the plasma membrane enriched fraction of the erythroblasts as differentiation proceeded. A majority of the newly synthesized proteins remain in the same proportion to each other during maturation; however, a few newly synthesized proteins greatly increase following EP induction while others decrease markedly. Of the radiolabeled proteins observed in two dimensional gels, only the spectrins, band 3 and actin become major proteins of the mature erythrocyte membrane. Examination of total proteins of the plasma membrane enriched fractions of EP-treated erythroblasts using silver staining and 32P autoradiography show that many proteins and phosphoproteins are selectively eliminated from this fraction late in the course of differentiation during the reticulocyte stage. The selective removal of many proteins at the reticulocyte stage of development combined with previous selective synthesis and accumulation of some specific proteins such as alpha and beta spectrin and band 3 in the differentiating erythroblasts lead to the final mammalian erythrocyte membrane structure.

The molecular basis of erythrocyte shape.

Recent discoveries about the molecular organization and physical properties of the mammalian erythrocyte membrane and its associated structural proteins can now be used to explain, and may eventually be used to predict, the shape of the erythrocyte. Such explanations are possible because the relatively few structural proteins of the erythrocyte are regularly distributed over the entire cytoplasmic surface of the cell membrane and because the well-understood topological associations of these proteins seem to be stable in comparison with the time required for the cell to change shape. These simplifications make the erythrocyte the first nonmuscle cell for which it will be possible to extend our knowledge of molecular interactions to the next hierarchical level of organization that deals with shape and shape transformations.

Fluorescence photobleaching recovery techniques for translational and slow rotational diffusion in solution and on cell surfaces.

Fluorescence photobleaching recovery techniques allow the accurate quantification of lateral and rotational motions of small numbers of specific molecules in complex systems. The technique was first applied to the study of translational diffusion in cell plasma membranes (Peters et al., 1974). This continues to be the principal area of application. More recently, it has been extended to the study of macromolecular diffusion, binding and polymerization in solution (e.g Barisas & Leuther, 1979; Lanni et al., 1981; Icenogle & Elson, 1983), and in situ, in the cytoplasm of living cells (e.g. Wojcieszyn et al., 1981; Wang et af . , 1982; Salmon et al., 1984). Fluorescence photobleaching analysis of slow rotational motion has generated considerable theoretical interest (e.g. Koppel, 1983; Wegener & Rigler, 1984; Wegener, 1984) but few experimental results to date (Johnson & Garland, 1981; Smith et af . , 1981; Jovin, 1986). Features and capabilities of the technique, emphasizing the analysis of translational diffusion, will be illustrated in this report with recent data from mammalian sperm cells and erythrocyte membranes.

Acetylcholinesterase release from mammalian erythrocytes by phosphatidylinositol-specific phospholipase C of Bacillus thuringiensis and characterization of the released enzyme.

The mode of acetylcholinesterase release from mammalian erythrocyte membranes by the action of phosphatidylinositol(PI)-specific phospholipase C of Bacillus thuringiensis was studied. As regards intact erythrocytes, a larger amount of acetylcholinesterase was released from sheep or bovine erythrocytes than from horse erythrocytes. From horse erythrocyte ghosts, acetylcholinesterase was more easily released than from intact cells. Bovine erythrocyte acetylcholinesterase released by PI-specific phospholipase C was purified by column chromatography on DEAE-cellulose, affinity gel and Sepharose 6B, to a homogeneous state, as indicated by polyacrylamide gel electrophoresis, with a recovery of 39%. Also, bovine erythrocyte acetylcholinesterase was solubilized by Triton X-100 and partially purified. The properties of these acetylcholinesterase preparations obtained by the action of PI-specific phospholipase C and/or Triton X-100 were studied in detail. On elution from the Sepharose 6B column, Triton X-100-solubilized acetylcholinesterase was eluted at the void volume while the enzyme obtained by further treatment with PI-specific phospholipase C was eluted in the region corresponding to M.W. 250,000. Furthermore, the heat stability of acetylcholinesterase purified after solubilization with PI-specific phospholipase C was higher than that of the Triton X-100-solubilized acetylcholinesterase. The close association and direct interaction of PI with acetylcholinesterase in the erythrocyte membrane was suggested by the above results.

Adsorption of sphingomyelinase of Bacillus cereus onto erythrocyte membranes

Sphingomyelinase of Bacillus cereus proved to be specifically adsorbed onto mammalian erythrocyte membranes in the presence of either Ca 2+ or Ca 2+ plus Mg 2+ in the order of sphingomyelin content; i.e., sheep, bovine > porcine > rat erythrocytes. No appreciable adsorption was observed in the presence of Mg 2+ alone nor in the absence of divalent metal ions. The enzyme adsorption onto bovine erythrocytes was dependent upon the incubation temperature. By shifting the temperature from 37 to 0 °C, sphingomyelinase once adsorbed onto the surface of bovine erythrocytes was released into the supernatant. Ca 2+ proved to be an essential factor for the enzyme adsorption: The addition of 1 m m Ca 2+ enhanced the adsorptive process, but inhibited sphingomyelin hydrolysis and hot or hot-cold hemolysis of erythrocytes, while the addition of 1 m m Ca 2+ plus 1 m m Mg 2+ enhanced sphingomyelin breakdown and hemolysis as well as the enzyme adsorption. However, when the amount of sphingomyelin fell off to 0.2–0.7 nmol/ml or less by the action of sphingomyelinase, the enzyme once adsorbed was completely released from the surface of erythrocytes. The result indicates that the major binding site for sphingomyelinase is sphingomyelin. In the presence of 1 m m Mg 2+ alone, the enzymatic hydrolysis of sphingomyelin and hemolysis proceeded whereas the enzyme adsorption was not encountered during 60 min incubation at 37 °C. The change in the molar ratio of Ca 2+ to Mg 2+ affected the enzyme adsorption and sphingomyelin breakdown; the higher Ca 2+ enhanced the adsorption whereas the higher Mg 2+ stimulated sphingomyelin hydrolysis.

Stepwise degradation of membrane sphingomyelin by corynebacterial phospholipases.

The mechanism of in vitro synergistic lysis of sheep erythrocytes by Corynebacterium ovis and Corynebacterium equi was investigated. Hemolysis required (i) the action of phospholipase D from C. ovis, (ii) the action of an extracellular protein of C. equi, and (iii) Mg2+. Maximum lysis required imposition on the system of a fourth condition (step iv), such as chilling. Steps i, ii, and iv occur sequentially and in that order. Mg2+ functions in steps i and ii. The extracellular protein C. equi was purified to homogeneity and found to be a phospholipase C capable of hydrolyzing ceramide phosphate, phosphatidic acid, and all of the isolated major phospholipids of mammalian erythrocyte membranes. The principal features of the synergistic hemolytic system could be reproduced in experiments involving liposomes containing either sphingomyelin or ceramide phosphate and trapped [14C]glucose. We inferred that sphingomyelin of sheep erythrocytes is first converted to ceramide phosphate by C. ovis phospholipase D. On the basis of results with liposomes, we propose that the ceramide phosphate is then converted to ceramide by C. equi phospholipase C. We believe that the resulting in situ ceramide then undergoes dislocation by chilling and perhaps also by virtue of an affinity between ceramide and C. equi phospholipase C. The dislocation of ceramide presumably disorganizes the lipid bilayer sufficiently to result in cell lysis.