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Biomedical subjects

D A Low

Publications and source records attributed to D A Low.

89 records · Page 5Linked to original sources
PubMed1989

Phase-variation of pyelonephritis-associated pili in Escherichia coli: evidence for transcriptional regulation.

The regulation of pyelonephritis-associated pili (pap) pilin gene transcription has been examined using two operons (pap-17 and pap-21) isolated from the pyelonephritogenic Escherichia coli strain C1212. DNA sequence analysis and E. coli minicell analysis were used to map two genes (papB and papI) within the pilin regulatory regions of both pap-17 and pap-21, and the protein products of these genes were identified. Pilin transcription, initiated at the papBA promoter, was monitored by constructing single copy operon fusions with lacZYA in E. coli K-12. Inoculation of E. coli (pap'-lac) strains onto solid M9 minimal medium containing glycerol and the Lac indicator X-gal (M9-Glycerol) yielded both Lac+ and Lac- colony phenotypes. The Lac+ ("phase on') and Lac- ("phase off') phenotypes were heritable since reinoculation of M9-Glycerol with bacteria picked from Lac+ colonies gave rise to a much higher fraction of Lac+ colonies than reinoculation of M9-Glycerol with bacteria picked from Lac- colonies. Measurement of phase transition rates for E. coli (pap17'-lac) inoculated onto M9-Glycerol showed that the Lac(-)----Lac+ transition frequency (1.57 X 10(-4)/cell/generation) was reduced 35-fold when cells were inoculated onto minimal medium containing glucose (M9-Glucose). However, the Lac+----Lac-transition frequency obtained using M9-Glycerol (2.60 X 10(-2)/cell/generation) was 1.4-fold lower compared to results obtained with M9-Glucose. In contrast, lowering the incubation temperature of E. coli (pap17'-lac) cultures from 37 degrees C to 23 degrees C caused all cells to shift to the Lac- state.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1988

Isolation and comparison of Escherichia coli strains from canine and human patients with urinary tract infections.

We analyzed Escherichia coli strains isolated from dogs with urinary tract infections (UTIs) in an attempt to determine if any of these strains were similar to E. coli isolated from humans with UTIs. Using genotypic and phenotypic traits, we identified four canine and six human E. coli UTI isolates that all appeared to be closely related or identical. All isolates shared similar DNA sequences for pyelonephritis-associated pili (pap), alpha-hemolysin (hly), and insertion sequence 5 (IS5), on the basis of Southern blot analysis. Similar outer membrane protein, pilin, and plasmid profiles were obtained for each of the isolates, although minor heterogeneity was observed. All of these isolates expressed a neuraminidase-sensitive binding phenotype in contrast to the majority of human isolates, which are known to express an adhesin that recognizes terminal digalactoside residues. Taken together, these results suggest that similar E. coli uropathogens may be capable of infecting both dogs and humans. To determine if the intestinal tracts of dogs were a reservoir for uropathogenic E. coli, eight paired rectal and urine pap+ E. coli strains were cultured from dogs with UTIs. By using the same genotypic and phenotypic criteria described above as a basis for strain identity, seven of eight urine-rectal pairs showed intrapair identity. However, each urine-rectal pair displayed a unique overall profile and could be distinguished from the other pairs. We conclude that the uropathogen colonizing the bladders of dog can also be the predominant strain colonizing the intestinal tracts.

Animals↗
PubMed1982

Cells regulate their mitogenic response to thrombin through release of protease nexin.

We previously reported that human and mouse fibroblast-like cells release into their growth medium a protein that we termed protease nexin. Protease nexin forms a covalent acyl linkage with thrombin and certain other serine proteases via the protease active site and mediates their binding, internalization and degradation by cells. Binding of thrombin-protease nexin to cells is mediated by the protease nexin portion of the complex to a high-affinity cellular binding site. As thrombin is a potent mitogen for a variety of fibroblast-like cells in culture, we examined whether protease nexin itself regulates thrombin-stimulated cell division. Recently, we showed that heparin virtually blocked the binding of thrombin-protease nexin complexes to both mouse and human cells without affecting the ability of these cells to respond to thrombin. Thus, protease nexin does not appear to be a positive modulator in thrombin-induced cell division. Here, we show that protease nexin negatively regulates the mitogenic response of cells in culture to thrombin.

Amyloid beta-Protein Precursor↗
PubMed1981

Released protease-nexin regulates cellular binding, internalization, and degradation of serine proteases.

Protease-nexin (PN), a component released by normal human fibroblasts into culture medium, forms covalent linkages with thrombin (Th) and the urinary plasminogen activator urokinase, apparently with their catalytic site serines. The present studies explored the function of PN by examining the interaction of protease-PN complexes with human fibroblasts and the consequences of this interaction. Th-PN and urokinase-PN complexes bind to cells via the PN portion of the complexes. The binding is selectively inhibited by heparin. Because PN has a heparin-binding site, this indicates that protease-PN complexes might bind to a cellular heparin-like site. After binding, the complexes are internalized. By inhibiting endocytosis with phenylarsine oxide, which does not affect cellular binding of Th-PN complexes, we showed that complexes must be internalized before they are degraded. Kinetic analysis of internalization and degradation of Th-PN showed that complexes are internalized more rapidly than they dissociate from the cell surface; by 120 min of incubation at 37 degrees C most cell-bound Th-PN complexes are degraded to amino acids. The results are summarized in a model showing how PN mediates the cellular binding, internalization, and degradation of serine proteases through formation of protease-PN complexes. This series of events may be involved in the regulation of serine protease activity at the cell surface and in the extracellular environment.

Amyloid beta-Protein Precursor↗
PubMed1980

Protease-nexin: a cellular component that links thrombin and plasminogen activator and mediates their binding to cells.

This report identifies a component of normal human fibroblasts that forms a covalent linkage with thrombin and urokinase (urinary plasmingoen activator) and mediates most of the specific cellular binding of these proteases. This component, here named protease-nexin (PN), is both associated with the cell surface and released into the culture medium. In several ways PN resembles antithrombin III (AT3), a prominent inhibitor of thrombin in serum: PN links thrombin, probably via an ester bond; PN does not link thrombin blocked at its catalytic site serine; PN has a high-affinity heparin-binding site; and heparin greatly accelerates the rate of linkage between soluble PN and thrombin. Despite these similarities, PN and AT3 are distinct; they differ in size and are not immunologically cross-reactive. Whereas AT3 regulates the proteolytic activity of thrombin in serum, PN may regulates the activity of serine proteases at and near the cell surface.

Amyloid beta-Protein Precursor↗
PubMed1977

Serological grouping of virulent and avirulent strains of the lobster pathogen Aerococcus viridans.

Virulent strains of Aerococcus viridans (formerly Gaffkya homari) are the aetiologic agents of gaffkemia, a septicaemic disease of the American lobster (Homarus americanus). The virulent and avirulent forms of this bacterium, previously thought to be taxonomically indistinguishable, have been differentiated by serological studies. Antisera were produced in rabbits using autoclaved bacteria as antigens. Reactions were measured by agglutination tests using microtitre techniques and an antigenic scheme was determined. Specific antisera were prepared by absorption and used to determine antigens of strains of A. viridans and other Gram-positive cocci. In general, only virulent strains of A. viridans have antigen b. Both virulent and avirulent strains possess other antigens also detected in strains of the genus Staphylococcus.

Agglutination Tests↗
PubMed1973

Membrane optical activity: some facts and fallacies.

The circular dichroism of hypothetical, water-filled, spherical shells, 75-3500 nm in radius, with walls 7.5 nm thick, composed of poly(L-lysine) in various conformational proportions, and suspended in water, were computed from the known optical properties of this polypeptide by classical general light-scattering theory (Mie theory). Comparison of the computed curves of circular dichroism spectra with those of diverse membranes reveals large discrepancies below 215 nm and shows that light scattering does not adequately account for the optical activity of membranes containing appreciable proportions of nonhelical conformation. However, turbidity effects can explain the anomalies of membrane optical rotatory dispersion near 233 nm, if not uniquely so. We conclude that the optical activity of neither most soluble proteins nor membrane proteins can provide accurate conformational information when synthetic polypeptides are used as standards and list the reasons for this argument. We also show that present techniques to "correct" membrane optical activity are likely to produce additional artifact.

Animals↗
PubMedDate not supplied

Dosimetry and techniques for simultaneous hyperthermia and external beam radiation therapy.

An increased biological effect is realized when hyperthermia and radiation therapy are combined simultaneously. To take advantage of this effect, techniques have been developed that combine existing hyperthermia devices with a linear accelerator. This allows concomitant delivery of either ultrasound or microwave hyperthermia with photon radiation therapy. Two techniques have been used clinically: the orthogonal technique, in which the microwave or ultrasound beam and the radiation beam are orthogonal to one another, and the en face technique, in which the ultrasound or microwave beam and the radiation beam travel into the tumour through the same treatment window. The en face technique has necessitated the development of special attachments so that the hyperthermia device can be mounted to the linear accelerator and so that non-uniform portions of the hyperthermia device can be removed from the radiation beam. For microwave therapy, applicators are mounted onto the linear accelerator using the compensating filter tray holder. For ultrasound, special reflector devices are mounted to a frame that is mounted onto the compensating filter tray holder of the linear accelerator. Because the linear accelerator is an isocentric device, the height of the radiation source is fixed, and this has necessitated specially designed devices so that the ultrasound support system is compatible with the linear accelerator. The treatment setups for both the en face technique and the orthogonal technique require the interaction of both hyperthermia and radiation therapy personnel and equipment. The dosimetry and day-to-day operations for each technique are unique. The simulation for the en face technique is much different from the simulation of a normal radiation treatment and requires the presence of a hyperthermia physicist. Also, for the en face technique, the attenuation of the microwave applicator and the thickness and attenuation of the ultrasound reflector system are taken into account for radiation dosimetry. This paper presents details of the dosimetry and logistics of the techniques for simultaneous thermoradiotherapy based on 7 years of experience treating more than 50 patients.

Cobalt Radioisotopes↗
PubMedDate not supplied

Electron bolus design for radiotherapy treatment planning: bolus design algorithms.

Computer algorithms to design bolus for electron beam radiotherapy treatment planning were investigated. Because of the significant electron multiple scatter, there is no unique solution to the problem of bolus design. However, using a sequence of operators, a bolus can be designed that attempts to meet three important criteria: adequate dose delivery to the target volume, avoidance of critical structures, and dose homogeneity within the target volume. Initial calculation of bolus shape was based upon creation operators forcing either the physical or the effective depths of the distal surface of the target volume to a specified value. Modification operators were then applied to the bolus to alter the shape to better meet the design criteria. Because the operators each address a single dosimetric issue, they can often adversely affect some other attribute of the dose distribution. In addition, an extension operator is used to design the bolus thickness outside the target volume. Application of these operators is therefore carried out in certain sequences and each may be used more than once in the design of a particular bolus. The effects of these operators on both the bolus and the resulting dose distribution are investigated for test geometries and patient geometries in the nose, parotid, and paraspinal region.

Algorithms↗