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Biomedical subjects

D Thomas

Publications and source records attributed to D Thomas.

At least 613 records · Page 34Linked to original sources
PubMed1990

The supramolecular organization of ovomucin. Biophysical and morphological studies.

Ovomucin participates in the ovomucin-gel-forming properties because of its shape and its ability to interact in a specific spatial organization. Purified from chicken egg-white by exclusion chromatography with Sephacryl S-300 and Sepharose CL-2B and analysed by light-scattering, it exhibited an Mr of about 40 x 10(6). This large Mr can be explained by the aggregation of polymers that can be degraded into 3 x 10(6)-Mr fragments by reduction with dithiothreitol. The values for hydrodynamic parameters such as Mr, radius of gyration, hydrodynamic radius, mass per unit length and combinations of them suggested that ovomucin is a linear and highly flexible molecule conferring upon it a random-coil-like structure in 0.2 M-NaCl solution. Analysis of the ovomucin molecules by electron microscopy revealed its linear character but also indicated a lower Mr than that obtained in the light-scattering experiments. By temperature-induced non-specific aggregation of an ovomucin solution containing other globular egg proteins, an attempt was made to find out what conditions are required for gel formation and to examine the quality of aggregation that is obtained under these conditions. Results show that the viscosity of the solution did not increase after heat treatment. Apparently, in the ovomucin gel, specific spatial organization of the ovomucin molecules is required for hydrogel formation.

Animals↗
PubMed1990

Measurement of oxygen concentration gradients in gel-immobilized recombinant Escherichia coli.

In this study, an oxygen microsensor was used to measure oxygen concentration profiles in carrageenan gel particles containing growing, immobilized Escherichia coli B (pTG201). Profiles, which were measured at intervals during continuous culture of gel slabs and beads, became increasingly steep with time. The oxygen penetration depth in the gel decreased with time, eventually reaching a steady state value of approximately 100 microns for both gel beads and slabs. A reaction-diffusion model employing zero-order cell growth kinetics was found to provide an excellent fit to the experimental concentration data. Growth rates estimated from profiles obtained during the first few hours of culture were 0.24h-1 (gel slabs) and 0.18h-1 (beads), compared to a value of 0.30 h-1 measured in free-cell suspensions at 25 degrees C.

Carrageenan↗
PubMed1990

Effect of free-cell growth parameters on oxygen concentration profiles in gel-immobilized recombinant Escherichia coli.

Oxygen concentration profiles in immobilized recombinant cells were measured using a microsensor. Experimental results showed that the final depth of oxygen penetration in the carrageenan gel was always in the range 80-100 microns for the strains and media used, although profiles of oxygen concentration during the early stages of cell growth depended on the strain and nutrient medium used. Variations in the oxygen profiles corresponded to differences in kinetic parameters measured for the same strains and media in free-cell experiments.

Carrageenan↗
PubMed1990

Agitation rate effects on plasmid stability in immobilized and free-cell continuous cultures of recombinant E. coli.

Escherichia coli B/pTG201 recombinant cells were immobilized by entrapment in a carrageenan gel and cultivated in nonselective media to investigate the effect of agitation rate on plasmid stability, biomass concentration, and enzyme productivity. These parameters were studied in continuous cultures for free and immobilized cells, respectively. Immobilized recombinant cells exhibit an increase in the stability of the plasmid pTG201 compared to free cells, even under conditions where the tendency of plasmid stability for free cells decreased generally more rapidly under a higher agitation rate. Intensive agitation, resulting also in a strong shear stress, greatly reduced cell concentration within gel beads throughout the course of growth. Higher enzyme expression of catechol 2-3, dioxygenase was also obtained in leaked cells due to better maintenance of plasmid stability and higher plasmid copy number with regard to free cells. Enzyme productivity of leaked and free cells in minimal medium decreased with the increase in agitation rate, due to decreased plasmid stability; however, in LB medium, it increased in the presence of higher agitation rate related to important cell concentration.

Catechol 2,3-Dioxygenase↗
PubMed1990

Water activity as a key parameter of synthesis reactions: the example of lipase in biphasic (liquid/solid) media.

Ester synthesis catalyzed by Candida cylindracea lipase (triacylglycerol acylhydrolase, EC 3.1.1.3) was investigated in solid/liquid biphasic media containing the enzyme preparation and reactants without addition of organic solvents not participating in the reaction. Although the effects of water on enzyme kinetics have been abundantly studied in nearly anhydrous media, reactions in which water is produced have not been investigated. The effect of water produced by the reaction itself on the enzymatic activity was studied. The dispersion of water in a shaken, nearly anhydrous medium was shown to be responsible for the lack of activity of the enzyme. In contrast, when slowly shaken, the enzyme was fully activated by the water furnished as a product of the reaction. However, when experiments were performed in a two-phase aqueous/organic system with previously solubilized enzyme in water, the enzyme activity was increased by shaking and was of the same order of magnitude as in nearly anhydrous media. Under low water activity conditions, a powerful agitation can lead to slower reaction rate, because water, a product of esterification, is not retained in the microenvironment of the enzyme to activate it. The activation effect of water produced by the reaction was clearly shown using enzyme preparations shaken in an anhydrous medium and previously equilibrated at low water activities (aw = 0.13 and 0.69). This activation did not occur for an enzyme preparation equilibrated at high aw (0.89) or for a preparation gently shaken in a water-saturated medium. The lag time preceding activation of the enzyme increased with the extent of enzyme dehydration.(ABSTRACT TRUNCATED AT 250 WORDS)

Candida↗
PubMed1990

Immobilized and free cell continuous cultures of a recombinant E. coli producing catechol 2,3-dioxygenase in a two-stage chemostat: improvement of plasmid stability.

The immobilization of recombinant strains of E. coli W3110/pTG205 in K-carrageenan gel beads improves the plasmid stability during continuous cultures in the absence of selection pressure. Since, xyl E gene (which encodes catechol 2,3-dioxygenase from Pseudomonas putida) transcription is controlled by the trp promoter, the effects of tryptophan (repressor) and 3 beta-indolyl acrylic acid (derepressor) on pTG 205 stability and enzyme production have been studied in both free and immobilized cell cultures. A two-stage continuous culture system running for 150 h is described. In the first stage an immobilized culture is performed in the presence of tryptophan with a significant plasmid stability. The cells released from the gel beads are continuously transferred in the second stage reactor where expression is induced by 3 beta-indolyl acrylic acid. In these conditions an efficient production of catechol 2,3-dioxygenase is observed.

Biotechnology↗
PubMed1990

Ifosfamide plus doxorubicin in previously untreated patients with advanced soft tissue sarcoma. The EORTC Soft Tissue and Bone Sarcoma Group.

The objective of this phase II trial was to assess the therapeutic activity and toxicity of doxorubicin plus ifosfamide in previously untreated patients with advanced soft tissue sarcoma. Treatment was doxorubicin 50 mg/m2 followed by a 24 h infusion of ifosfamide 5 g/m2 plus mesna 2.5 g/m2 repeated every 3 weeks until disease progression or unacceptable toxicity occurred. Of 203 patients entered, 175 were evaluable for response. The response rate was 35% (95% CI 28-42%), with 9% of the patients achieving a complete remission and 26% a partial remission. The median time to progression was 29 weeks for all evaluable patients, and 67, 40 and 28 weeks for complete and partial responders and patients with stable disease, respectively. The median duration of survival was 58 weeks. Myelosuppression was the dose-limiting toxicity, resulting in leukopenia (WHO grade 3 and 4) in 73% of evaluable treatment courses. Other side-effects were rare and usually well manageable.

Adolescent↗
PubMed1990

Child survival, height for age and household characteristics in Brazil.

"The impact of household characteristics on child survival and height, conditional on age, is examined using household survey data from Brazil. Parental education is found to have a very strong positive effect on both outcomes and this is robust to the inclusion of household income and also parental heights, which partly proxy for unobserved family background characteristics. We find that income effects are significant and positive for child survival but insignificant for for child height although the latter depends on identification assumptions. Parental height has a large positive impact on child height and on survival rates even after controlling for all other observable characteristics."

Age Factors↗
PubMed1990

An improved strategy for generating a family of unidirectional deletions on large DNA fragments.

A modification of the Barnes "kilo-sequencing" method is described. The procedure presented here makes it possible to obtain a series of nested deletions on large DNA fragments in only two days. It applies to double-stranded DNA, and thus can be used with plasmids as well as the M13mp series of bacteriophages. The main improvements are the use of a second restriction enzyme, which makes it possible to begin the deletions at any site on the DNA fragment, and the use of mung bean nuclease for trimming the DNA edges so that any restriction enzyme can be used. This method, using a pUC vector and sequencing on double-stranded DNA, would make it possible to read a DNA nucleotide sequence on both strands starting with only one construction.

Base Sequence↗
PubMed1990

Impact of the Special Supplemental Food Program on infants.

The Special Supplemental Food Program for Women, Infants, and Children, popularly known as WIC, provides participants with supplemental foods and nutrition education. The WIC participants are eligible pregnant, postpartum, and breast-feeding women, infants, and children up to their fifth birthday. The program currently serves 1.2 million infants each month. The U.S. Department of Agriculture National WIC Evaluation Study of Infants and Children is the most comprehensive assessment of WIC's impact on a national infant sample. Its findings indicate that WIC infants consumed more iron-fortified infant formula (the core of the WIC infant food package) than non-WIC infants and, as a result, had higher daily intakes of formula-related nutrients--namely, iron and vitamin C. Because of lower consumption of whole cow milk, WIC infants had lower daily intakes of milk-related nutrients--calcium, protein, magnesium, and vitamin B6. The research team concluded that increased dietary intake of specific nutrients occurs only during program participation and has no residual effect after participation ceases. Possible scientific and social science research that would be useful in federal policy decisions affecting infant participation in the WIC program is discussed.

Child, Preschool↗
PubMed1990

Activation of the inflammatory response of neutrophils by Tamm-Horsfall glycoprotein.

The activation of human polymorphonuclear leukocytes (PMN) by particulate Tamm-Horsfall glycoprotein (THG) represents an interaction hitherto unrecognized. The potential pathophysiological effect of this phenomenon within the interstitium of the kidney is highlighted by the activation of the respiratory burst, as well as by comprehensive PMN degranulation. Products of the interaction are expressed in terms of phagocytosis, luminol-dependent chemiluminescence, granule marker enzyme release and arachidonic acid metabolism. Significant quantities of the primary, secondary and tertiary granule markers, myeloperoxidase, vitamin B12 binding protein and N-acetyl-beta-D-glucosaminidase, respectively, were secreted in a dose and time-dependent manner. Phagocytosis of the glycoprotein was accompanied by the generation of significant quantities of leukotriene B4. Furthermore, the ability of such a particulate ligand to activate the alternative pathway of complement clearly represents a capacity to augment the inflammatory response. Should the interaction of THG with PMN take place within the interstitium of the kidney, augmented by the deposition of complement proteins on the surface of insoluble aggregates, the resulting inflammatory response may lead to marked tissue damage and eventually result in interstitial fibrosis.

Complement Pathway, Alternative↗
PubMed1990

Stimulation of a human T-cell clone with anti-CD3 or tumor necrosis factor induces NF-kappa B translocation but not human immunodeficiency virus 1 enhancer-dependent transcription.

The expression of transiently transfected expression vectors under the control of the long terminal repeat (LTR) of the human immunodeficiency virus (HIV) or its enhancer sequence and the translocation of the HIV enhancer-binding protein NF-kappa B were analyzed in two human T-cell clones stimulated through their T-cell receptor complex or by tumor necrosis factor or phorbol 12-myristate 13-acetate. We found a dissociation of NF-kappa B translocation from transactivation of either the HIV LTR or the HIV enhancer. Interleukin 2 induced proliferation but not NF-kappa B translocation or LTR transactivation. Phorbol ester or specific antigen recognition induced HIV LTR transactivation, whereas stimulation with tumor necrosis factor or antibody to CD3 did not. The two latter signals were nevertheless able to induce NF-kappa B translocation with a pattern in the band-shift assay indistinguishable from that observed using phorbol ester. Our finding that induction of NF-kappa B by tumor necrosis factor or antibody to CD3 is not sufficient to induce HIV enhancer-dependent transcription in cloned T cells contrasts with results obtained in most lymphoblastoid T-cell lines and indicates that normal T lymphocytes differ from tumoral T cells in terms of requirements for HIV LTR activation. Furthermore, our results suggest that events linked to T-cell activation, in addition to NF-kappa B translocation per se, induce functional interactions of the NF-kappa B complex with the HIV enhancer.

Antibodies↗
PubMed1990

Characteristics of the tyrosine recognition signal for internalization of transmembrane surface glycoproteins.

A tyrosine residue in the cytoplasmic domain of a class of cell surface receptors is necessary, but not sufficient, for internalization through coated pits. To identify the amino acid context enabling a tyrosine to serve as a signal for endocytosis, we mutated the short cytoplasmic domain of a mutant influenza virus hemagglutinin that is competent for internalization, HA-Y543, and determined the effect of each change on internalization. From these results and a comparison of sequences of other proteins recognized by coated pits, a "tyrosine internalization signal" was proposed. Site-directed mutagenesis was employed to insert complete, or incomplete "tyrosine internalization signals" into the cytoplasmic domain of a protein normally not endocytosed, human glycophorin A. Only the complete signal caused internalization of mutant glycophorins by coated pits. The signal is formed by a short amino acid sequence, with polar or basic residues preferred at certain positions on either side of the tyrosine. Amino acids, which in proteins of known structure are frequently found in turns, are clustered near the tyrosine on the side of the signal nearest the transmembrane domain.

Amino Acid Sequence↗
PubMed1990

An experimental model for salpingitis due to Chlamydia trachomatis and residual tubal infertility in the mouse.

A mouse model of salpingitis and subsequent tubal infertility induced by a human strain of Chlamydia trachomatis has been studied. C3H/He female mice were inoculated into the ovarian bursa. Some of the mice (six infected, five controls) were killed on days 15 and 23 and the remaining animals (10 infected, 10 controls) were mated on day 15. On day 15, the infection was maximal with intratubal inflammation, elevated antichlamydial antibody titre and positive cultures in 12 cases out of 16. After 19 weeks of housing with the male, the proportion of fertilized females was significantly lower in the infected group (20% versus 100% in the control group P less than 0.01). In the killed mice, hydrosalpinx and or tubal occlusion were noted at this time in nine cases out of 10, despite an apparent bacteriological healing.

Animals↗