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Biomedical subjects

L S Avigad

Publications and source records attributed to L S Avigad.

7 recordsLinked to original sources
PubMed1979

A cytolytic protein from the edible mushroom, Pleurotus ostreatus.

Aqueous extracts of the edible mushroom, Pleurotus ostreatus, contain a substance that is lytic in vitro for mammalian erythrocytes. The hemolytic agent, pleurotolysin, was purified to homogeneity and found to be a protein lacking seven of the amino acids commonly found in proteins. In the presence of sodium dodecyl sulfate it exists a monomers of molecular weight 12 050 whereas under non-dissociating conditions it appears to exist as dimers. It is isoelectric at about pH 6.4. The sensitivity of erythrocytes from different animals correlates with sphingomyelin content of the erythrocyte membranes. Sheep erythrocyte membranes inhibit pleurotolysin-induced hemolysis and the inhibition is time and temperature dependent. Ability of membranes to inhibit hemolysis is abolished by prior treatment of membranes with specific phospholipases. Pleurotolysin-induced hemolysis is inhibited by liposomes prepared from cholesterol, dicetyl phosphate and sphingomyelin derived from sheep erythrocytes whereas a variety of other lipid preparations fail to inhibit. It is concluded that sphingomyelin plays a key role in the hemolytic reaction.

Agaricales↗
PubMed1979

Nature and mechanism of action of the CAMP protein of group B streptococci.

The extracellular product of group B streptococci responsible for the CAMP reaction was purified to near homogeneity. It is a relatively thermostable protein having a molecular weight of 23,500 and an isoelectric pH of 8.3. It was found that the CAMP reaction could be simulated by substituting [14C]glucose-containing liposomes prepared from sphingomyelin, cholesterol, and dicetyl phosphate for sheep erythrocytes. In the belief that the liposome system is a valid model, the mechanism of the CAMP reaction was further investigated by using liposomes in which N-acylsphingosine (ceramide) was substituted for sphingomyelin. In this system disruption of liposomes, as measured by release of trapped [14C]glucose, was effected by CAMP protein alone. As judged from thin-layer chromatography, CAMP protein caused no reduction in the amount of ceramide present in ceramide-containing liposomes, nor were split products demonstrable. However, binding of CAMP protein to ceramide-containing liposomes could be shown. It is inferred that in sheep erythrocytes CAMP protein reacts nonenzymatically with membrane ceramide formed by the prior action of staphylococcal sphingomyelinase and that binding of CAMP protein to ceramide disorganizes the lipid bilayer to an extent that results in cell lysis.

Amino Acids↗
PubMed1978

Inhibition of hemolysis by zinc and its reversal by L-histidine.

Hemolysis induced by staphylococcal alpha-toxin, staphylococcal beta-toxin, streptolysin O, and streptolysin S was inhibited by zinc ions by virtue of inhibition of an early step in the events leading to lysis, presumably by preventing the lysins from attaching to the plasma membrane. In contrast, in hemolysis induced by Clostridium perfringens alpha-toxin and by perfringolysin O, a later step was inhibited by zinc. In hemolysis caused by saponin, lysolecithin, and Triton X-100, hemoglobin was precipitated by zinc ions as it was released from the erythrocyte. Inhibition by zinc was abolished by several amino acids of which L-histidine was the most effective.

Animals↗
PubMed1976

Properties of a toxin from the sea anemone Stoichacis helianthus, including specific binding to sphingomyelin.

Stoichactis helianthus toxin, a protein derived presumably from the nematocysts, was purified to homogeneity. It has a molecular weight of about 16,000, an isoelectric pH of 9.8, and it contains approximately 3.7% carbohydrate. It is powerfully hemolytic for erythrocytes derived from a variety of animal species, those of the cat being the most sensitive and those of the guinea pig the most resistant. The toxin is lytic also for rabbit blood platelets, and it destroys cultured fibroblasts but is inactive for several kinds of bacterial protoplasts and spheroplasts. The hemolytic activity is specifically inhibited by sphingomyelin, and it is proposed that this phospholipid is the constituent of the membrane which functions as receptor for the toxin. Supporting evidence includes the findings that enzymes known to destroy sphingomyelin (a) prevent erythrocyte membranes from inhibiting hemolysis, and (b) render erythrocytes resistant to lysis by the toxin. The mechanism underlying hemolysis may involve translocation of membrane sphingomyelin by virtue of a specific affinity of the coelenterate protein for this phospholipid.

Animals↗
PubMed1976

Inhibition by zinc of hemolysis induced by bacterial and other cytolytic agents.

Zinc, cupric, and cadmium ions, in that order of effectiveness, inhibited lysis of washed, rabbit erythrocytes by the toxic bacterial product aerolysin. Hemolysis induced by a variety of other lytic agents was also inhibited by Zn2+ in approximately the same concentration as that, 0.33 mM, needed to inhibit aerolysin-induced hemolysis. Zinc ions did not inhibit osmotic lysis. Inhibition requires the continues presence of Zn2+ and apparently involves a readily reversible binding of Zn2+ to the cell surface, which, it is postulated is accompanied by a reversible alteration in the state of the lipid bilayer.

Animals↗
PubMed1975

Interactions between aerolysin, erythrocytes, and erythrocyte membranes.

Aerolysin, a hemolytic and lethal exotoxin of Aeromonas hydrophila, was analyzed for amino acids. Assuming 8 histidine residues/mol, the purified toxic protein has, by summation, a molecular weight of 49,000, a value in agreement with earlier estimates by other methods. Erythrocytes from different animal species differ greatly in sensitivity to aerolysin's lytic action. There is some correlation between sensitivity and phosphatidyl choline content. Erythrocyte membranes of different species bind the toxin, and the efficiency of binding is a function of sensitivity to lysis. Binding is temperature independent, is not dependent upon membrane sialic acid, and is decreased by prior treatment with phospholipase C and proteases. Preparations of aerolysin convert substantial amounts of membrane phosphorus to water-soluble form; the conversion is concentration and temperature dependent. Most of the conversion is attributable to contaminating phospholipase(s) that is separable from the toxin. Aerolysin purified by electrophoresis in polyacrylamide gel retains some phospholipase activity, and this activity may or may not be a contaminant.

Aeromonas↗