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Biomedical subjects

K Burton

Publications and source records attributed to K Burton.

88 records · Page 5Linked to original sources
PubMed1967

Oxidation of pyrimidine nucleosides and nucleotides by osmium tetroxide.

1. Pyrimidine nucleosides such as thymidine, uridine or cytidine are oxidized readily at 0 degrees by osmium tetroxide in ammonium chloride buffer. There is virtually no oxidation in bicarbonate buffer of similar pH. Oxidation of 1-methyluracil yields 5,6-dihydro-4,5,6-trihydroxy-1-methyl-2-pyrimidone. 2. Osmium tetroxide and ammonia react reversibly in aqueous solution to form a yellow 1:1 complex, probably OsO(3)NH. A second molecule of ammonia must be involved in the oxidation of UMP since the rate of this reaction is approximately proportional to the square of the concentration of unprotonated ammonia. 3. 4-Thiouridine reacts with osmium tetroxide much more rapidly than does uridine. The changes of absorption spectra are different in sodium bicarbonate buffer and in ammonium chloride buffer. They occur faster in the latter buffer and, under suitable conditions, cytidine is a major product. 4. Polyuridylic acid is oxidized readily by ammoniacal osmium tetroxide, but its oxidation is inhibited by polyadenylic acid. Pyrimidines of yeast amino acid-transfer RNA are oxidized more slowly than the corresponding mononucleosides, especially the thymine residues. Appreciable oxidation can occur without change of sedimentation coefficient.

Chromatography↗
PubMed1966

Selective degradation of thymidine and thymine deoxynucleotides.

1. Osmium tetroxide in dilute ammonia oxidizes various pyrimidine nucleosides at different rates. Thymidine is oxidized about 45 times as fast as deoxycytidine. The phosphate groups may be eliminated from oxidized thymine nucleotides by successive treatments with alkali and then with diphenylamine in aqueous formic acid. The reactions can be applied to the selective degradation of thymidine in oligodeoxynucleotides.

Alkalies↗
PubMed1966

Fractionation of deoxyribonucleic acid from phage-infected bacteria.

1. DNA has been isolated in 90% yield from T5-infected cultures of Escherichia coli ;pulse'-labelled with [(3)H]thymidine. It had a buoyant density in caesium chloride solution identical with the DNA of mature T5 phage, and no components of unusual buoyant density were detected. 2. The DNA preparation was resolved into two major components of differing specific activity on a column of kieselguhr coated with methylated serum albumin. The DNA of high specific activity could be eluted from the column only with 2n-ammonia, and the firm binding did not appear to be due to an artifact of preparation. 3. A similar fractionation into two DNA components of differing specific activity was observed when the ;pulse'-labelled culture was lysed with sodium dodecyl sulphate and the lysate rocked with phenol. The DNA of high specific activity was found in the interface precipitate between the phenol and aqueous layers. 4. The amounts of DNA in the two fractions were measured at different times after infection and the radioactivity content of each was determined at various times after a short ;pulse' of [(3)H]thymidine. The interface fraction contained the replicating phage DNA, and the DNA from mature phage particles appeared in the aqueous fraction. 5. Analogous results were obtained with T2-infected E. coli. In the presence of chloramphenicol the DNA in the interface fraction was not converted into DNA extractable into the aqueous layer. Since chloramphenicol prevents the condensation of DNA into phage heads, it is suggested that any DNA in extended configuration is trapped inside the rigid-layer framework of the cell wall. 6. Treatment with lysozyme released much of the DNA from the interface precipitate. This DNA was firmly bound by the chromatographic column and had the same buoyant density in caesium chloride solution as normal T5-phage DNA. Sucrose-gradient sedimentation studies showed that it was heterogeneous and that as much as 60% sedimented faster than T5-phage DNA.

Chemical Phenomena↗
PubMed1965

The integrity of deoxyribonucleic acid extracted from Escherichia coli 15T after thymine-less death.

1. The integrity of DNA extracted from Escherichia coli strain 15T(-) after thymine-less death was examined by studying the effects of treatment with aqueous alkali on the solubility in dilute acids and by viscosity and ultracentrifugal measurements, some of which were designed to detect single-strand breaks or inter-strand cross-links. None of the results showed that there was any modification or damage associated with thymine-less death.

Journal Article↗
PubMedDate not supplied

Potential of machine-vision light microscopy in toxicologic pathology.

Major developments in machine-vision light microscopy and in reagent chemistry have led to a renaissance and revolution in the use of the light microscope in biology, biotechnology, and medicine. The potential use of this technology in the field of toxicologic pathology is discussed. It is suggested that a combination of investigating living cells and tissues and fixed samples using the new technologies will lead to understanding mechanisms of toxicity. Examples of the use of the methods in basic cell biology and medicine are presented.

Animals↗
PubMedDate not supplied

Effect of gamma-irradiation on peptide-containing hydrophilic poly (d,l-lactide-co-glycolide) microspheres.

The effect of gamma-irradiation on the physicochemical properties of peptide-containing hydrophilic poly (d,l-lactide-co-glycolide) (PLGA) microspheres was evaluated. PLGA (50/50, Mw: 8,600) with free carboxylic end groups was used to make drug-loaded and placebo microspheres by a solvent extraction evaporation method. Both formulated and non-formulated microspheres were gamma-irradiated at 0, 1, 1.5, and 2.5 Mrad doses. HPLC analysis based on extraction of peptide from the microspheres showed that peptide content of the microspheres was lowered upon irradiation and the reduction was more pronounced in formulated microspheres. The in-vitro release in 0.033M phosphate buffer, pH 7.0 at 37 degrees C (based on extraction of residual peptide) showed that the initial and subsequent release of peptide was higher in gamma-irradiated microspheres during the first 20 days. The difference became insignificant during the erosional controlled release of the peptide. There was no difference in release between the formulated and non-formulated microspheres of the nonirradiated or irradiated forms. Molecular weights (Mw and Mn), determined by size exclusion chromatography, were reduced by gamma-irradiation for both formulated and non-formulated placebo microspheres. Differential scanning calorimetry showed a gradual reduction in Tg of placebo microspheres but no reduction in peptide-loaded microspheres. In-vivo evaluation of the nonirradiated and the 1.5 Mrad irradiated microspheres showed no marked differences through 28 days. Since irradiation caused a lowering of Mw and Mn with the appearance of a low amount of unidentified substances, seemingly catalyzed by the polymer and the formulation excipients, gamma-irradiation sterilization of these parenteral delivery systems requires careful investigation on an individual product basis.

Gamma Rays↗
PubMedDate not supplied

Prescribing medications and malpractice suits: clear, consistent documentation is the key.

The information provided in this article should not be construed as all encompassing. It is not intended to be legal advice. It is intended to be a risk management presentation of certain aspects of claims data, treands, systems and processes in order to better equip physicians and office personnel in recognizing, preventing and controlling medication-related incidents.

Documentation↗