Search PubMed⌕ Search

Biomedical subjects

R J Doyle

Publications and source records attributed to R J Doyle.

At least 145 records · Page 8Linked to original sources
PubMed1976

Inactivation of membrane transport in Escherichia coli by near-ultraviolet light.

Evidence is presented that near-ultraviolet (near-UV) light can alter galactoside transport in Escherichia coli in several independent ways. It can inactivate the permease system per se, it can interfere with metabolic energy production or transfer, and it can cause an increase in the generalized permeability of the membrane. Earlier publications suggested that near-UV destroys cofactors needed for electron transport and thus places a limitation on energy reserves. In agreement, we found that the active accumulation of [14C]thiomethyl-beta-D-galactopyranoside is decreased after irradiation by a larger factor than that due to action directly on the permease system. The effect on the latter was measured by the decrease in the rate of o-nitrophenyl-beta-D-galactopyranoside (ONPG) transport. As evidence that energy supplies for this "downhill" process did not become rate limiting after irradiation, we found that carbonylcyanide-m-chlorophenyl-hydrazone did not stimulate ONPG transport of irradiated cells. Cells genetically deficient in functional permease or cells treated with formaldehyde still transport ONPG passively, although at much lower rates. With the use of such cells, it was found that high fluences (doses) made the cells leaky. Further evidence that the permease system and the metabolic energy system can be inactivated independently is also presented. It is shown that a photoproduct from the irradiation of chloramphenicol inactivates the permease system much more efficiently than the energy system. In addition, it is shown that thio-beta-D-digalactopyranoside protects the permease system, but not the energy system, both against direct inactivation by near-UV and against photosensitized inactivation in the presence of chloramphenicol.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1976

A circular test pattern for evaluating x-ray tube focal spots.

The design and use of a circular x-ray resolution test pattern is presented. This pattern is shown to yield equivalent focal spot dimensions equal to those obtained with the more commonly used star pattern. The advantage of using the circular pattern is that it obviates the necessity of positioning the pattern strictly along the x-ray beam central axis. A major source of experimental error in making focal spot measurements is therefore circumvented, especially in the case of x-ray tubes with a small target angle.

Mathematics↗
PubMed1975

Organization of teichoic acid in the cell wall of Bacillus subtilis.

The phytohemagglutinin, concanavalin A (Con A), interacts specifically and reversibly with the polyglucosyl glycerol phosphate teichoic acid of Bacillus subtilis 168 cell walls. Advantage has been taken of this interaction to examine the organization of the surface teichoic acid at the ultrastructural level. Con A-treated whole cells and cell walls contain an irregular, fluffy layer 25 to 60 nm thick which is absent in untreated or alpha-methyl glucoside-treated preparations. This discontinuous layer is present only on the outer profile of Con-A-treated cell walls. The surface teichoic acid is proposed to be oriented perpendicular to the long axis of the cell. Fixation and embedment for electron microscopy result in condensation of this layer which then contributes to the stainable portion of the wall. Con A treatment binds adjacent teichoic acid molecules in their native configuration producing the irregular, fluffy layer visualized.

Bacillus subtilis↗
PubMed1975

Distribution of teichoic acid in the cell wall of Bacillus subtilis.

Hydrolysis of the cell wall of Bacillus subtilis 168 by autolysins or lysozyme resulted in the exposure of glucosylated teichoic acid molecules as evidenced by increased precipitation of [14C] concanavalin A. The number of concanavalin A-reactive sites increased significantly after only limited enzymatic digestion of the walls. Quantitative analyses of [14C] concanavalin A-treated wall or wall hydrolysate complexes indicate that approximately one-half of the teichoic acid molecules are surface-exposed, whereas the remainder are probably embedded within the peptidoglycan matrix. Treatment of the cell walls with sodium dodecyl sulfate or Triton X-100 did not result in new concanavalin A-reactive sites. Partial autolysis diminished the ability of the cell walls to adsorb bacteriophage phi25. Fluorescein-labeled concanavalin A bound intensely over the entire surface of growing B. subtilis 168 cells, suggesting that teichoic acid molecules are located on the total solvent-exposed surface area of the bacteria.

Adsorption↗
PubMed1975

Soluble macromolecular complexes involving bacterial teichoic acids.

Cell wall and membrane teichoic acids from several bacteria formed soluble complexes with polysaccharides and bovine plasma in alkyl alcohol solutions. Polysaccharides which contain different monomeric units and anomeric configurations complexed with the teichoic acids, suggesting that the interaction is relatively nonspecific. Teichoic acids complexed glycogen or bovine plasma albumin in 50 to 97% ethanol solutions. The macromolecular association between teichoic acids and polysaccharides or proteins was independent of teichoic acid size over a threefold molecular weight range. Glycerol phosphates or an acid hydrolysate of teichoic acid would not complex to either glycogen or bovine plasma albumin in ethanol. The optimal interaction between glycogen and the Bacillus subtilis lipoteichoic acid occurred between pH 4.5 and 8.2. The ability of teichoic acids to bind polysaccharides and proteins in moderate dielectric constant solvents suggests that these polymers may serve as complexing agents for hydrophilic molecules found in membranes.

Bacillus subtilis↗
PubMed1974

Polyelectrolyte nature of bacterial teichoic acids.

Several physicochemical properties of the teichoic acid of Bacillus subtilis 168 have been determined. The teichoic acid partial specific volume was found to be 0.57 ml/g. The apparent weight-average molecular weight of the polymer was 24,800. Sedimentation was strongly dependent on solvent. The sedimentation coefficient of the teichoic acid was found to have a value of s(20.w) (0) = 1.90S. In dilute buffers and distilled water, the teichoic acid possessed a rigid rod or extended conformation. Salts induced a loss of secondary structure in the polymer, resulting in a random coil configuration. Salt-induced structural changes in the teichoic acid were determined by viscosities, ultraviolet difference spectra, and inhibition of precipitation with concanavalin A. Divalent cations such as Mg(2+) had little effect on the teichoic acid structure. The salt-induced structural changes were reversible, as evidenced by return of the original properties upon dialysis of the teichoic acid against water. Sodium chloride inhibited the adsorption of bacteriophage ø25 to B. subtilis cell walls. Teichoic acid conformation may have a significant influence on the physiology of bacteria.

Adsorption↗
PubMed1973

Modification of bacteriophage phi 25 adsorption to Bacillus subtilis by concanavalin A.

The phytohemagglutinin, concanavalin A (Con A), interacts specifically and reversibly with the alpha-d-glucose-substituted polyglycerol phosphate teichoic acids of Bacillus subtilis 168. Teichoic acids from nonglucosylated strains (mutants resistant to phage phi25) interact weakly, if at all, with Con A. Prior treatment of glucosylated cell walls with Con A results in a concentration-dependent inhibition of phage phi25 adsorption. The inhibition of adsorption to glucosylated cell walls occurs immediately upon the formation of the Con A-cell wall complex and is reversed upon dissociation of the complex by addition of alpha-methyl glucose. Examination of the interaction between Con A and whole cells, cell walls, or wall digests from glucosylated (phage-sensitive) and non-glucosylated (phage-resistant) strains further demonstrates the specificity of the reaction. A conditional phage phi25-resistant mutant only forms complexes with Con A when grown under permissive conditions.

Adsorption↗
PubMed1973

Facilitated diffusion of monosaccharides in Saccharomyces cerevisiae: experimental investigation of kinetic parameters without the assumptions of symmetry.

Until the question of symmetry or asymmetry in the facilitated diffusion of monosaccharides by Saccharomyces cerevisiae is resolved, attempts to study the transport process cannot be based on assumptions of symmetry, such as equal concentrations at equilibrium or kinetic parameters that are equal in opposite directions. The assumptions of symmetry may be circumvented by measuring efflux against water and against various external concentrations of sugar. The measurement of efflux against water eliminates any involvement of influx, and the separate determinations of influx and efflux parameters do not require that the parameters be equal. Furthermore, the use of relative internal concentrations eliminates any necessity of assuming that the equilibrium concentrations are equal. Since the influx and efflux parameters are to be compared, the measurement of influx on effluxing cells allows both sets of parameters to be determined on cells which are physiologically the same. This procedure has been tested by obtaining the kinetic parameters of l-sorbose transport. The validity of these parameters was demonstrated by using them to generate theoretical efflux curves that fit the experimental data and by showing that they give the best fit curve to the relationship of velocity and permeant concentration. Although the question of symmetry remains unanswered, this procedure has opened the way for experimental evaluation of the situation and further investigation of the transport process in yeast.

Biological Transport↗
PubMed1972

Interaction of concanavalin A with the cell wall of Bacillus subtilis.

Interactions between concanavalin A and cell wall digests of Bacillus subtilis 168 resulted in insoluble complexes as observed by double gel diffusion, turbidity, and analysis of the precipitate. The macromolecular constituent of the cell walls complexing with concanavalin A was the polyglucosylglycerol phosphate teichoic acid. The complex exhibited two pH optima: 3.1 and 7.4. The complex could be dissociated by saccharides which bind to concanavalin A. In contrast to concanavalin A-neutral polysaccharide complexes, formation of the concanavalin A-wall complex was inhibited by salts. It was subsequently shown that salts induce conformational changes in cell wall digests. The data suggested that for complex formation to occur a rigid rod conformation in the glucosylated teichoic acid is probably necessary. Concanavalin A can be used as a probe to study structural features of bacterial cell walls.

Autolysis↗