HEMOLYSIS OF RABBIT ERYTHROCYTES BY PURIFIED STAPHYLOCOCCAL ALPHA-TOXIN. III. POTASSIUM RELEASE

Development of a luciferase-based Gram-positive bacterial reporter system for the characterization of antimicrobial agents

Mechanistic investigations are of paramount importance in elucidating the modes of action of antibiotics and facilitating the discovery of novel drugs. We reported a luciferase-based reporter system using bacterial cells to unveil mechanisms of antimicrobials targeting transcription and translation. The reporter gene Nluc encoding NanoLuciferase (NanoLuc) was integrated into the genome of the Gram-positive model organism, Bacillus subtilis, to generate a reporter strain BS2019. Cellular transcription and translation levels were assessed by quantifying the amount of Nluc mRNA as well as the luminescence catalyzed by the enzyme NanoLuc. We validated this system using three known inhibitors of transcription (rifampicin), translation (chloramphenicol), and cell wall synthesis (ampicillin). The B. subtilis reporter strain BS2019 successfully revealed a decline in Nluc expression by rifampicin and NanoLuc enzyme activity by chloramphenicol, while ampicillin produced no observable effect. The assay was employed to characterize a previously discovered bacterial transcription inhibitor, CUHK242, with known antimicrobial activity against drug-resistant Staphylococcus aureus. Production of Nluc mRNA in our reporter BS2019 was suppressed in the presence of CUHK242, demonstrating the usefulness of the construct, which provides a simple way to study the mechanism of potential antibiotic candidates at early stages of drug discovery. The reporter system can also be modified by adopting different promoters and reporter genes to extend its scope of contribution to other fields of work.

IMPORTANCE

Discovering new classes of antibiotics is desperately needed to combat the emergence of multidrug-resistant pathogens. To facilitate the drug discovery process, a simple cell-based assay for mechanistic studies is essential to characterize antimicrobial candidates. In this work, we developed a luciferase-based reporter system to quantify the transcriptional and translational effects of potential compounds and validated our system using two currently marketed drugs. Reporter strains generated in this study provide readily available means for identifying bacterial transcription inhibitors as prospective novel antibacterials. We also provided a series of plasmids for characterizing promoters under various conditions such as stress.

Bacillus thuringiensis Cyt2Aa2 toxin disrupts cell membranes by forming large protein aggregates

We show that the lipid membrane disruption by Bacillus thuringiensis (Bt) Cyt2Aa2 is different from the general pore-forming model. Cyt2Aa2 forms protein aggregates that disrupt the lipid membrane integrity.

Bacillus thuringiensis (Bt) Cyt2Aa2 showed toxicity against Dipteran insect larvae and in vitro lysis activity on several cells. It has potential applications in the biological control of insect larvae. Although pore-forming and/or detergent-like mechanisms were proposed, the mechanism underlying cytolytic activity remains unclear. Analysis of the haemolytic activity of Cyt2Aa2 with osmotic stabilizers revealed partial toxin inhibition, suggesting a distinctive mechanism from the putative pore formation model. Membrane permeability was studied using fluorescent dye entrapped in large unilamellar vesicles (LUVs) at various protein/lipid molar ratios. Binding of Cyt2Aa2 monomer to the lipid membrane did not disturb membrane integrity until the critical protein/lipid molar ratio was reached, when Cyt2Aa2 complexes and cytolytic activity were detected. The complexes are large aggregates that appeared as a ladder when separated by agarose gel electrophoresis. Interaction of Cyt2Aa2 with Aedes albopictus cells was investigated by confocal microscopy and total internal reflection fluorescent microscopy (TIRF). The results showed that Cyt2Aa2 binds on the cell membrane at an early stage without cell membrane disruption. Protein aggregation on the cell membrane was detected later which coincided with cell swelling. Cyt2Aa2 aggregations on supported lipid bilayers (SLBs) were visualized by AFM. The AFM topographic images revealed Cyt2Aa2 aggregates on the lipid bilayer at low protein concentration and subsequently disrupts the lipid bilayer by forming a lesion as the protein concentration increased. These results supported the mechanism whereby Cyt2Aa2 binds and aggregates on the lipid membrane leading to the formation of non-specific hole and disruption of the cell membrane.

Distinct mechanisms for K+ efflux, intoxication, and hemolysis by Bordetella pertussis AC toxin

Adenylate cyclase (AC) toxin from Bordetella pertussis delivers its catalytic domain to the interior of target cells where it converts host ATP to cAMP in a process referred to as intoxication. This toxin also hemolyzes sheep erythrocytes by a mechanism presumed to include pore formation and osmotic lysis. Intoxication and hemolysis appear at strikingly different toxin concentrations and evolve over different time scales, suggesting that different molecular processes may be involved. The present study was designed to test the hypothesis that intoxication and hemolysis occur by distinct mechanisms. Although the hemolytic activity of AC toxin has a lag of >1 h, intoxication starts immediately. Because of this difference, we sought a surrogate or precursor lesion that leads to hemolysis, and potassium efflux has been observed from erythrocytes treated with other pore-forming toxins. AC toxin elicits an increase in K+ efflux from sheep erythrocytes and Jurkat cells, a human T-cell leukemia line, that begins within minutes of toxin addition. The toxin concentration dependence along with the analysis of the time course suggest that toxin monomers are sufficient to elicit release of K+ and to deliver the catalytic domain to the cell interior. Hemolysis, on the other hand, is a highly cooperative event that likely requires a subsequent oligomerization of these individual units. Although induction of K+ efflux shares some structural and environmental requirements with both intoxication and hemolysis, it can occur under conditions in which intoxication is reduced or prevented. The data presented here suggest that the transmembrane pathway by which K+ is released is separate and distinct from the structure required for intoxication but may be related to, or a precursor of, that which is ultimately responsible for hemolysis.

Analysis of the lytic activity of the Serpulina hyodysenteriae hemolysin

The hemolysins of Serpulina hyodysenteriae are active at 27 to 40 degrees C and pH 3 to 9 and are unaffected by enzymatic inhibitors. Pore formation was demonstrated by the inhibition of hemolysis with molecules of 2.0 to 2.3 nm in diameter and the release of 86rubidium from erythrocytes without hemoglobin release after exposure to native hemolysin.

STAPHYLOCOCCAL ALPHA-HEMOLYSIN: DETECTION ON THE ERYTHROCYTE MEMBRANE BY IMMUNOFLUORESCENCE

Purified staphylococcal alpha-hemolysin (but not the toxoid) was demonstrated on the surface of rabbit and human erythrocytes by immunofluorescence. This occurred during the period of maximal hemolysis and was a transient event. These findings have been analyzed in relation to previous data on the kinetics of leakage of both small and complex molecular constituents of the erythrocyte.

HEMOLYSIS OF RABBIT ERYTHROCYTES BY PURIFIED STAPHYLOCOCCAL ALPHA-TOXIN. II. EFFECTS OF INHIBITORS ON THE HEMOLYTIC SEQUENCE

Cooper, Louis Z. (New England Center Hospital, Boston, Mass.), Morton A. Madoff, and Louis Weinstein. Hemolysis of rabbit erythrocytes by purified staphylococcal alpha-toxin. II. Effect of inhibitors on the hemolytic sequence. J. Bacteriol. 87:136-144. 1964.-Study of the time course of hemolysis of rabbit erythrocytes by purified staphylococcal alpha-lysin revealed that the specific toxin-red cell reaction occurs during the prelytic period. This reaction could be prevented or decreased by alpha-lysin antitoxin added early, but not by antitoxin added at the end of the prelytic phase or at any time thereafter. In contrast, hemolysis is suppressed temporarily by sucrose and permanently by polyethylene glycol, even when these are added during the period of rapid release of hemoglobin. When sucrose is present together with alpha-lysin and red cells only during the prelytic period, and when the cells are then washed and resuspended in phosphate-buffered saline, their subsequent hemolysis is not altered by the presence of the sugar. This is not so when antitoxin is employed. When erythrocytes are laked by a measured excess of alpha-lysin, only a portion of the original hemolytic activity can be recovered. Repeated exposure of lysin to red cells produces a loss of activity represented by a linear function when logs of residual activity are plotted sequentially. Once alpha-lysin has reacted with red cells, it does not appear to be available for attachment to other erythrocytes.

Mechanism of action of Moraxella bovis hemolysin

Bovine erythrocytes (RBCs) exposed to Moraxella bovis culture supernatants exhibited rapid leakage of intracellular K+ (95% in 10 min), slower cell swelling (1.20-fold increase in mean corpuscular volume in 20 min), and subsequent lysis (76% leakage of hemoglobin in 25 min). Incubation media made hypertonic by the addition of 75 mM carbohydrates with molecular diameters of 0.72 to 1.32 nm prevented hemolysin-induced RBC swelling, but incubation media made hypertonic by the addition of carbohydrates with molecular diameters of less than 0.72 nm did not protect against hemolysin-induced RBC swelling. Raffinose (75 mM; molecular diameter, 1.14 nm) did not block hemolysin-induced K+ leakage but did block hemolysis. These findings support the hypothesis that hemolysin-induced lysis occurs by colloid-osmotic swelling and are compatible with M. bovis hemolysin acting as a pore-forming cytolysin. Assuming that M. bovis hemolysin acts as a transmembrane molecular sieve, then the functional size of the hemolysin transmembrane pores in bovine RBCs is approximately 0.9 nm, the molecular size of sucrose. Hemolytic activity was inhibited by the Ca2+ chelator ethylene glycol-bis (beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), but hemolysin-induced K+ leakage was not affected by EGTA.

Effect of Escherichia coli hemolysin on permeability of erythrocyte membranes to calcium

The extracellular hemolysin produced by porcine strains of E. coli effects a marked increase in the calcium permeability of erythrocyte membranes. This hemolysin promotes both calcium efflux from either calcium-loaded erythrocytes or erythrocyte ghosts and calcium accumulation during the pre-lytic period. Erythrocyte membrane calcium permeability was determined using either the radioisotope 45Ca or a calcium electrode. When similar concentrations of erythrocytes (35% packed cell volume) were treated with increasing amounts of hemolysin there was an increase in both the rate and the extent of calcium accumulation by the erythrocytes. These increases were due to increased numbers of erythrocytes becoming permeable to calcium as hemolysin concentrations increased, rather than increasing amounts of calcium being accumulated by individual erythrocytes. Hemolysins produced by porcine strains of E. coli from five geographical areas all increased calcium permeability of erythrocyte membranes.

Conformational alteration in alpha-toxin from Staphylococcus aureus concomitant with the transformation of the water-soluble monomer to the membrane oligomer

The membrane-damaging alpha-toxin aggregate of Staphylococcus aureus was characterized physicochemically. The aggregate weight of the toxin formed by various methods appeared to be 6 times higher than the molecular weight of the monomer as determined by the laser light scattering technique, suggesting the presence of a hexamer in the membrane. The aggregates fluoresced 20 to 50% more than the monomer at 336 nm. Circular dichroism measurements revealed that both the monomer and the oligomer showed essentially beta-sheet structure with the maximum ellipticity about -8,400 deg.cm2.dmol-1 at 215 nm. Circular dichroism spectrum of the oligomers showed ellipticity difference of -6,600, -44 and +84 deg.cm2.dmol-1, at 200, 250 and 280 nm, respectively, compared with the monomer. All these results suggest that the conformational change in the toxin molecule occurs concomitant with the transformation of the water-soluble monomer to the membrane-embedded hexamer.

Effect of calcium ions on staphylococcal alpha-toxin-induced hemolysis of rabbit erythrocytes

Calcium in millimolar concentrations protected rabbit erythrocytes from hemolysis caused by staphylococcal alpha-toxin. This effect was maximal at 30 mM CaCl2 and required the continued presence of calcium. The protection was not absolute and could be overcome by increased concentrations of alpha-toxin. Calcium did not block the binding of alpha-toxin to erythrocytes but inhibited the alpha-toxin-induced release of small ions from the cell as measured by 86Rb release. The transient removal of calcium was sufficient to abrogate its protective effect, suggesting that its action involves a reversible alteration in the state of the membrane. The three steps of the alpha-toxin-induced hemolytic sequence are: (i) binding to specific receptors, (ii) formation of transmembrane pores, and (iii) cell lysis. We concluded that calcium acted at step ii by impeding the lateral movement of alpha-toxin necessary to form the transmembrane hexamer pores.

Osmotic stabilizers differentially inhibit permeability alterations induced in Vero cells by Clostridium perfringens enterotoxin

Using a sensitive Vero (African green monkey kidney) cell model system, studies were performed to further investigate whether Clostridium perfringens enterotoxin acts via disruption of the colloid-osmotic equilibrium of sensitive cells. Enterotoxin was shown to cause a rapid loss of intracellular 86Rb+ (Mr approx. 100) with time- and dose-dependent kinetics. The enterotoxin-induced release of intracellular 86Rb+ preceded the loss of two larger labels, 51Cr label (Mr approx. 3500) and 3H-labeled nucleotides (Mr less than 1000). The osmotic stabilizers, sucrose and poly(ethylene glycol), differentially inhibited enterotoxin-induced larger label loss versus 86Rb+ loss. Further, enterotoxin was shown to cause a rapid influx of 24Na+ that was not significantly inhibited by osmotic stabilizers. Additional studies demonstrated that lysosomotropic agents were not protective against characteristic enterotoxin-induced membrane permeability alterations or morphological damage. Taken collectively, these results are consistent with an action for enterotoxin which involves a disruption of the osmotic equilibrium.

Effect of staphylococcal alpha-hemolysin upon anion transport in the rabbit erythrocyte

Equilibrium exchange of SO4(2-) was measured prior to and during hemolysis in rabbit erythrocytes exposed to staphylococcal alpha-hemolysin. The anion-transport protein of the rabbit erythrocyte has also been identified. Equilibrium exchange of SO4(2-) was measured by both efflux and influx of 35SO4(2-). The rate of influx of SO4(2-) in rabbit erythrocytes exposed to alpha-hemolysin was twice that of the untreated cells. The rate of SO4(2-) efflux was unchanged by alpha-hemolysin. Inhibition of anion exchange with 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) did not inhibit hemolysis, therefore, the increased influx of SO4(2-) may occur through a DIDS-insensitive pathway.

Action of staphylococcal alpha-toxin on membranes: some recent advances

Recent developments in the area of Staphylococcal alpha-toxin studies are presented which modify the concepts previously held with respect to both biological and physical properties of alpha-toxin. New data concerning the nature of the binding site for alpha-toxin on rabbit erythrocyte membranes and a model to explain the various observed complexes of alpha-toxin and membrane receptor are discussed. Finally, evidence suggesting that Staphylococcal alpha-toxin is a potent demyelinating agent is presented.

The interaction of bee melittin with lipid bilayer membranes

The influence of melittin and the related 8-26 peptide on the stability and electrical properties of bilayer lipid membranes is reported. Melittin, unlike the 8-26 peptide, has a dramatic influence on lipid membranes, causing rupture at dilute concentrations. The circular dichroism of melittin demonstrated that under physiological conditions, in water, melittin is in extended conformation, which is enhanced in aqueous ethanol. However in 'membrane-like' conditions it is essentially alpha-helical. Secondary structure predictions were used to locate possible alpha-helical nucleation centres and a model of melittin was built according to these predictions. It is postulated that melittin causes a wedge effect in membranes.

Studies on the binding of staphylococcal 125I-labeled alpha-toxin to rabbit erythrocytes

Staphylococcal alpha-toxin, a hemolytic exotoxin, can be iodinated using the lactoperoxidase method. 125 I-Labeled alpha-toxin binds to rabbit erythrocytes in an apparently irreversible and highly specific manner. The binding of 125 I-labeled alpha-toxin to erythrocytes of rabbit and human reflects the species specificity of native alpha-toxin. Binding of 125I-labeled alpha-toxin is blocked by the presence of native alpha-toxin, 127I-labeled alpha-toxin, or anti-alpha-toxin antibody. Simultaneous assays of 125I-labeled alpha-toxin binding and leakage of intracellular 86Rb+ suggest that toxin binding and membrane damage are separate, sequential functions. Both the rate and extent of binding are temperature dependent. Rabbit erythrocytes possess 5 X 10(3) binding sites/cell, while human erythrocytes possess no detectable binding sites. Treatment of rabbit erythrocytes with 125I-labeled alpha-toxin appears to decrease the number of unoccupied binding sites. Chaotropic ions can inhibit 125I-labeled alpha-toxin binding and cause bound 125I-labeled alpha-toxin to dissociate from rabbit erythrocyte membranes. Treatment of intact rabbit erythrocytes with pronase reduces both the binding capacity of the cells for 125I-labeled alpha-toxin, and the cells' sensitivity to hemolysis by native alpha-toxin. It is proposed that the primary binding site for alpha-toxin in biomembranes is a surface membrane protein.

Sensitive assay for detection of toxin-induced damage to the cytoplasmic membrane of human diploid fibroblasts

A sensitive assay was developed for detection and quantitation of subtle permeability changes in the cytoplasmic membrane of human diploid fibroblasts. Release of the non-metabolizable amino acid [1-14C]alpha-aminoisobutyric acid (AIB; molecular weight (103) from the cytoplasm of prelabeled cells was used as an indicator of toxin-induced membrane damage. An optimal procedure for labeling these cells was designed after varying the conditions with regard to pH, temperature, concentration of AIB, composition of medium, and incubation time. Toxin-induced release of AIB was compared with release of a previously described nucleotide label, [3H]uridine. Melittin from bee venom and the polyene antibiotics filipin and amphotericin B in low concentrations induced a strikingly greater release of AIB than of nucleotide label. The sensitivity of this assay was furthermore demonstrated by treatment with the following bacterial cytolysins: phospholipase C and theta-toxin from Clostridium perfringens, alpha-, beta-, delta-, and gamma-toxins from Staphylococcus aureus, and streptolysin S from Streptococcus pyogenes. In spite of their different modes of action, all these membrane-active toxins at low concentrations induced a significant release of AIB label. For an equal release of nucleotide label, several times higher concentrations were required.

Characteristics of streptolysin O hemolysis: kinetics of hemoglobin and 86rubidium release

The characteristics of hemolysis produced by streptolysin O (SLO) were investigated in rabbit, human, and rat erythrocytes. Kinetic studies of hemoglobin (Hb) release showed that rabbit and human erythrocytes exhibited typical "multi-hit" survival curves. Extrapolation of these curves to the ordinate indicated that approximately two molecules of SLO may be sufficient to produce lysis of a single cell. In contrast, exponential ("single-hit") survival curves were observed when rat erythrocytes were treated with SLO. At 0 C, high concentrations of SLO rapidly lysed rabbit erythrocytes; low concentrations had no effect on the cells at this temperature. The release of intracellular (86)rubidium ((86)Rb(+)) and Hb in rabbit erythrocytes exposed to SLO was investigated. In the presence of phosphate-buffered saline, rubidium and Hb were lost at the same rate from toxin-treated cells. The addition of bovine serum albumin to the suspending medium did not retard the escape of Hb, and the efflux of (86)Rb(+) only slightly preceded Hb loss. Addition of sucrose to the cells delayed both Hb and rubidium release. These results are interpreted as indicating that the "colloid-osmotic" lytic process is not involved in the hemolysis of erythrocytes by streptolysin O.

Effects of purified staphylococcal alpha toxin on the ultrastructure of human and rabbit erythrocytes

Previous studies have suggested that the primary site of action of purified staphylococcal alpha toxin is the cell membrane. Scanning and transmission electron microscopy studies were undertaken, therefore, to define toxin-induced alterations in the surface morphology of rabbit and human red blood cells. During the prelytic lag phase, scanning electron microscopy revealed multiple discrete blisters on the surface of rabbit red blood cells; during hemolysis, cellular collapse and ghosts were seen, but most striking was the separation of large fragments of cell membrane from red blood cell surfaces. In contrast, alterations in less sensitive human red blood cells were limited to occasional fingerlike protrusions during the period of accelerated lysis. Transmission electron microscopy substantiated these changes. These studies have provided further evidence that the cell membrane is the primary site of action of staphylococcal alpha toxin.

Effect of purified staphylococal alpha toxin on active sodium transport and aerobic respiration in the isolated toad bladder

Purified staphylococcal alpha toxin was found to inhibit the active transport of sodium across the isolated toad bladder when applied to the serosal but not to mucosal surface. Heating or the addition of specific antitoxin abolished this effect. Low temperatures reduced this activity significantly. Application of vasopressin to the bladder serosa shortly after toxin resulted in only weak and transient stimulation of sodium transport; once maximal toxin activity had been established, exposure to the hormone was without effect. Transport in bladders previously stimulated by vasopressin was rapidly inhibited by alpha toxin. Concentrations that suppressed active sodium transport completely within 30-45 min produced a significant increase in oxygen consumption by minced bladder tissue within the same period; antitoxin neutralized this activity. 2,4-dinitrophenol also inhibited sodium transport and stimulated oxygen consumption by the toad bladder. The addition of 2,4 dinitrophenol to bladder tissue in which respiration was maximally stimulated by alpha toxin resulted in a further increase in respiratory rate. The addition of toxin to bladder tissue after its exposure to a concentration of 2,4 dinitrophenol known to uncouple oxidative phosphorylation produced a significant stabilization but no increment in respiratory rate. The data are consistent with the previously suggested action of staphylococcal alpha toxin on cell membranes and suggest that energy-dependent transport processes are inhibited. The stimulation of oxygen consumption may be due to an additional effect on oxidative phosphorylation.

Inhibition of staphylococcal alpha-toxin. A kinetic evaluation of aromatic polysulphonic acids as inhibitors of haemolysis

1. The effect of a number of aromatic polysulphonic acids on the kinetics of haemolysis of rabbit erythrocyte suspensions by crude staphylococcal alpha-toxin was studied at pH8.6 and 6.8. 2. All of the inhibitory compounds caused an increase in the prelytic lag time (tau) of the sigmoid haemolysis curves, an increase in the time to reach 50% haemolysis (t((1/2))) and a decrease in the maximum rate of haemolysis (R(max.)). The most inhibitory compounds caused a 50% decrease in R(max.) at concentrations between 0.1 and 0.2mm. 3. The effect of pH varied considerably: compounds (I) and (II) were almost equally inhibitory at both pH values, compounds (IV) and (IX) were more inhibitory at pH6.8 than at pH8.6, and compounds (VII), (VIII), (X), (XI) and (XII) were more inhibitory at pH8.6. 4. Increased time of premixing alpha-toxin with compound (I) caused increased inhibition. 5. An attempt was made, where possible, to relate the inhibitory activity to the structure of the test compound.

Interaction of staphylococcal alpha-toxin with artificial and natural membranes

Comparison of hemolytic activity and chromate-releasing activity of partially purified preparations of staphylococcal alpha-toxin indicated the presence of a lytic factor other than alpha-toxin. This lytic release factor (RF) was isolated from the preparations and was shown to be active against both lipid spherules and erythrocytes. Heat-purified alpha-toxin (HP alpha-toxin) disrupted spherules, with the formation of fragments which always showed the presence of ring structures similar in dimensions (ca. 90 A) to pure alpha 12S-toxin. The interaction of HP alpha-toxin with spherules was accompanied by loss of hemolytic activity and adsorption of toxic protein. The alpha 12S-toxin, although only weakly hemolytic, was shown to be lytic for spherules. An alpha 12S-free toxin rapidly disrupted spherules, with formation of fragments with attached rings similar in dimensions to the alpha 12S molecule. Lipid monolayer experiments showed that HP alpha-toxin could penetrate lipid monolayers by virtue of a hydrophobic interaction. Effects of HP alpha-toxin on rabbit and human erythrocyte ghosts were similar to its effects on spherules, in that rings appeared on membrane fragments. Toxin-lysed rabbit erythrocytes showed similar rings on the resulting membrane fragments. However, rings were not seen on toxin-treated rabbit erythrocytes in the prelytic lag phase; this result and the fact that human erythrocytes are largely insensitive to alpha-toxin were interpreted as evidence against a lytic mechanism involving ring formation as the primary event. Rings were interpreted as toxin polymers similar to alpha 12S molecules, formed from specifically orientated active toxin molecules at the surface of lipid structures. Possible mechanisms for toxin lysis of spherules and erythrocytes are discussed.

Purified staphylococcal alpha toxin: effect on epithelial ion transport

Purified staphylococcal alpha toxin, when added to the serosal bathing medium of the isolated toad bladder, causes a rapid fall in short-circuit current and transepithelial potential difference. It has no effect when added to the mucosal bathing medium. Oxygen consumption by suspensions of minced bladder tissue is stimulated by the toxin. These effects are neutralized by staphylococcal antitoxin.

Staphylococcal alpha-toxin: effects on artificial lipid spherules

Staphylococcal alpha-toxin induces the release of previously sequestered anions or glucose from artificial phospholipid spherules, an effect abolished by specific antitoxin. Alphatoxin resembles streptolysin S in releasing anions or glucose from spherules prepared without cholesterol, and can be distinguished from the membrane-active polyene amphotericin B, which preferentially disrupts spherules containing cholesterol. It may affect biological structures by a similiar interaction with membrane phospholipids.