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Biomedical subjects

J H Freer

Publications and source records attributed to J H Freer.

At least 37 records · Page 2Linked to original sources
PubMed1986

Antigenic heterogeneity in subunit S1 of pertussis toxin.

Culture supernates containing pertussis toxin (PT) from four strains of Bordetella pertussis were examined for both immunological reactivity and biological activity. PT from all four strains sensitized mice to histamine and toxin was detectable in supernates of all strains when examined by Western blotting with polyclonal antiserum to PT. In supernates of three of the four strains, PT was detectable by an enzyme-linked immunosorbent assay (ELISA) using mouse monoclonal antibody to subunit S1 of PT as the third antibody layer. However, supernates from one strain, 18323, failed to react in ELISA. Electroblots probed with the monoclonal antibody labelled subunit S1 of PT from all strains except that of strain 18323. PT of strain 18323, whilst retaining histamine-sensitizing activity, differed antigenically from that of other strains.

Antigens, Bacterial↗
PubMed1985

One-dimensional peptide mapping of the subunits of pertussis toxin.

Pertussis toxin (pertussigen) purified from the cytoplasmic fraction of Bordetella pertussis strain 18334, phase 1, consisted of five subunits which included an additional subunit (S1a) not previously reported. Subunits S1, S1a and S2 showed extensive structural homology when analysed by one-dimensional peptide mapping, indicating that the latter two were probably derived from proteolytic cleavage of the largest subunit, S1. Subunits S3 and S4,5 generated only a limited number of peptides following chemical and enzymic degradation, but these subunits differed structurally from each other and from those showing structural homology.

Bacterial Toxins↗
PubMed1984

Binding of 125I-alpha toxin of Staphylococcus aureus to erythrocytes.

Alpha toxin purified from Staphylococcus aureus strain Wood 46 and radioiodinated by the lactoperoxidase method retained full haemolytic activity and was used to study factors affecting binding to rabbit and horse erythrocytes. A relatively fixed percentage of added toxin bound to both cell types; the percentage bound was independent of temperature, pH, cell concentration and toxin concentration. Neither a 50-fold excess of native toxin nor Concanavalin A inhibited the binding of iodinated toxin to erythrocytes. The results suggest that differences in the sensitivity of erythrocytes to haemolysis do not reflect the abundance of high affinity toxin receptors on sensitive cells, but are more probably the result of differences in the intrinsic stability of the membrane and its sensitivity to perturbation by amphiphilic agents.

Animals↗
PubMed1984

Inhibition of secretion of staphylococcal alpha toxin by cerulenin.

Secretion of alpha toxin by Staphylococcus aureus strain Wood 46 was preferentially inhibited by cerulenin, an antibiotic that stops fatty-acid synthesis by inhibiting beta-keto acyl acyl carrier-protein synthetase. At the concentrations used, cerulenin had a negligible effect on cell growth and total protein synthesis, but reduced lipid synthesis by 50%. Extracellular and membrane-associated alpha toxin was absent in cultures treated with cerulenin, but toxin formation was resumed after either removal of the antibiotic or addition of exogenous fatty acids. The apparent absence of toxin precursor in membranes of inhibited cells favours inhibition at an earlier stage in toxin synthesis.

Antifungal Agents↗
PubMed1982

Interaction of Staphylococcus aureus delta-lysin with phospholipid monolayers.

The interactions of purified staphylococcal delta-lysin and melittin with various phospholipid monolayers containing different polar head groups and fatty acid moieties and with monolayers of cod and sheep erythrocyte lipids at various initial film pressures (pi i) were studied by using the Wilhelmy plate method. In each case the final increase in surface pressure (delta pi) was a linear function of pi i. In the case of delta-lysin, the critical pressures (pi c, the extrapolated values of pi i at delta pi = 0) for phosphatidylcholines with different fatty acid chain length, dipalmitoylphospholipids with different polar head groups, and cod or sheep erythrocyte total lipids fell within a relatively narrow range whereas melittin showed a much wider range. The collapse pressures of the delta-lysin and melittin films at the air-water interface when adsorbed from the hypophase were very similar. delta-Lysin showed little or no specificity in its interactions with all types of lipid films studied, whereas melittin showed preferential interaction with films of acidic lipid, similar to the specificity reported for cardiotoxins of Naja mossambica mossambica described by other workers.

Animals↗
PubMed1982

Cytolytic toxins and surface activity.

Surface-active properties of alpha-toxin and delta-lysin, two cytolytic protein exotoxins of the bacterium Staphylococcus aureus are summarised. The relevance of differences in surface charge density on membranes is discussed in relation to possible mechanisms of binding and membrane penetration by alpha-toxin. An hypothesis for the mechanism of membrane disruption by delta-lysin involving the formation of hydrophilic transmembrane pores is proposed.

Amino Acid Sequence↗
PubMed1979

Location of binding sites on common type 1 fimbriae from Escherichia coli.

Common type 1 fimbriae were isolated from Escherichia coli and their length distribution profile was determined before and after treatment with ultrasound. As fimbriae were shortened, so their haemagglutinating capacity decreased, but their ability to bind to erythrocytes did not decrease to the same extent. Isolated fimbriae did not agglutinate inside-out vesicles prepared from horse erythrocytes or liposomes, suggesting that the binding mechanism was not based on non-specific hydrophobic interactions. The results support a lateral rather than a terminal location for the fimbrial binding site responsible for haemagglutination.

Binding Sites↗
PubMed1975

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.

Binding Sites↗
PubMed1972

Isolation and properties of mesosomal membrane fractions from Micrococcus lysodeikticus.

1. A method is described for the isolation of pure mesosomal membrane fractions from Micrococcus lysodeikticus. 2. Plasmolysis of cells, before wall digestion, was necessary for effective mesosome release. 3. The effect of mild shearing forces, temperature and time upon the release of mesosomal membrane from protoplasts was investigated. 4. The optimum yield of mesosomal membranes from stable protoplasts was achieved at 10mm-Mg(2+). 5. Mesosomal membrane vesicle fractions prepared at differing Mg(2+) concentrations above 10mm were similar in chemical composition. 6. Comparison of the properties of peripheral and mesosomal membrane fractions revealed major differences in the distribution of protein components, membrane phosphorus, mannose and dehydrogenase activities between the two fractions. 7. Only cytochrome b(556) was detected in mesosomal membranes, whereas peripheral membranes contained a full complement of cytochromes. 8. Preliminary investigations suggested the localization of an autolytic enzyme(s) in the mesosomal vesicles. 9. The anatomy of mesosomal and peripheral membrane have been compared by the negative-staining and freeze-fracture technique. 10. The results are discussed in relation to a plausible role for the mesosome.

Bacterial Proteins↗
PubMed1970

Factors influencing the activity of succinate dehydrogenase in membrane preparations from Micrococcus lysodeikticus.

1. Some properties of succinate dehydrogenase [succinate-(acceptor) oxidoreductase, EC 1.3.99.1] in membrane preparations from Micrococcus lysodeikticus (N.C.T.C. 2665) were investigated. 2. In the spectrophotometric assay system adopted the reaction velocity was shown to be proportional to the amount of membrane added. Dichlorophenol-indophenol, reduced photochemically in the presence of phenazine methosulphate, or enzymically by the membrane-bound enzyme, was shown to undergo reoxidation in the dark. 3. The membrane-bound enzyme was found to be inactivated at temperatures above 10 degrees C. 4. The specific activity of membrane-bound succinate dehydrogenase was found to increase between two- and three-fold in diluted membrane preparations equilibrated at 0 degrees C for 6h. Membranes treated with sodium deoxycholate showed no enzyme activation on dilution but displayed maximal activity, all activity being sedimentable at 103000g. The increase in specific activity observed on dilution could be partially inhibited by fixation with glutaraldehyde, or by the presence of bovine serum albumin. 5. The addition of Mg(2+) or Ca(2+) ions to membrane suspensions caused an overall depression of enzyme activity. 6. The results suggest the presence of an ;inhibitor' that affects the expression of membrane bound succinate dehydrogenase activity.

Aldehydes↗