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Biomedical subjects

J H Freer

Publications and source records attributed to J H Freer.

46 records · Page 3Linked to original sources
PubMed1968

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.

Adsorption↗
PubMed1967

Fine structure of Bacillus megaterium during microcycle sporogenesis.

Ultrathin sections were prepared from cultures of Bacillus megaterium QM B1551 undergoing microcycle sporogenesis (initial spore to primary cell to second-stage spore without intervening cell division) on a chemically defined medium. The cytoplasmic core of the dormant spore was surrounded by plasma membrane, cell-wall primordium, cortex, outer cortical layer, and spore coats. Early in the cycle, the coat opened at the germinal groove, the cortex swelled, ribosomes and a chromatinic area associated with large mesosomes (which may later be incorporated into the expanding plasma membrane) appeared in the core, and the cell wall became defined at the site of the cell wall primordium. Poly-beta-hydroxybutyrate granules began to appear in the primary cell at about 3 hr. By 7 hr, the forespore of the second-stage spore was delineated by typical double membranes. Between 7 and 12 hr, second-stage cell-wall primordium and cortex developed between the separating forespore membranes. The inner membrane became the plasma membrane of the second-stage spore, and the outer membrane eventually disintegrated within the second-stage spore cortex. A densely staining double layer (spore-coat primordium) developed external to the outer forespore membrane. The inner spore coat and the outer cortical layer of the second-stage spore developed from this primordium. The outer part of the spore coat, probably of sporangial origin, was laid down on the external surface of the inner spore coat. By 12 hr, second-stage spores were almost mature. By 20 hr, the mature endospores, with a thickened outer coat, were often still enclosed by degenerate primary cell wall and by the outer cortical layer and spore coat of the initial spore.

Bacillus megaterium↗
PubMed1967

Physical states of staphylococcal alpha-toxin.

At least three different forms of staphylococcal alpha-toxin have been shown to exist: soluble active alpha-toxin (alpha 3S), soluble inactive alpha-toxin (alpha(12s)), and insoluble inactive aggregate. Aggregation to the insoluble, biologically inactive form could be induced by brief heating to 60 C. The aggregate was dissociated by treatment with 8 m urea with reappearance of biological activity. Subsequent removal of urea by dialysis resulted in some spontaneous reaggregation to the insoluble state. The supernatant fluid obtained after dialysis contained soluble active alpha-toxin of high specific activity, possessing physical, toxic, and immunological properties closely resembling those of native toxin. The soluble biologically inert component (alpha(12s)) was identified as a third physical state. Negatively stained preparations of this material, when examined in the electron microscope, showed rings of approximately 100 A outside diameter containing 6 +/- 1 subunits.

Bacterial Proteins↗
PubMed1966

Inhibition of Sindbis virus plaque formation by extracts of Escherichia coli.

Vilcek, Jan (New York University School of Medicine, New York, N.Y.), and John H. Freer. Inhibition of Sindbis virus plaque formation by extracts of Escherichia coli. J. Bacteriol. 92:1716-1722. 1966.-Extracts prepared from washed cells of Escherichia coli B by sonic treatment and subsequent filtration through a 0.45-mu membrane filter significantly inhibited plaque formation with Sindbis virus in cultures or primary chick embryo cells up to a dilution of 1:20,000. The inhibitor acted on the cells rather than directly on the virus. The inhibiting substance was nondialyzable. Treatment of crude extracts with nucleases, trypsin, chymotrypsin, pepsin, or ether had no effect on the activity. Treatment with pronase destroyed the virus-inhibiting effect. Extracts prepared from two strains of E. coli B and one strain of E. coli K-12 all showed inhibitory activity against Sindbis virus. The inhibitor was present in the cytoplasmic fraction of bacteria. It was also active against Sindbis virus in human cells and showed some activity against vesicular stomatitis and vaccinia viruses in different types of cells. Interferon was not shown to be involved in the inhibition, although actinomycin D partially reversed the inhibitory activity of the extracts.

Chymotrypsin↗