Search PubMed⌕ Search

Biomedical subjects

E D Bransome

Publications and source records attributed to E D Bransome.

At least 19 recordsLinked to original sources
PubMed1987

Initial studies of a phytoestrogen-deoxyribonucleic acid interaction.

Molecular modeling studies show that estrogens such as estradiol complement the topography of spaces between base pairs in unwound DNA and simultaneously hydrogen bond phosphate moieties on opposite strands. We demonstrate here that the phytoestrogen coumestrol has this capability, in addition to its documented properties of UV absorbance at lambda greater than 300 nm and fluorescence. The latter properties enable spectroscopic examination of interactions with DNA by methods not possible with estrogenic steroids. On exposure to calf thymus DNA, the UV spectrum of coumestrol displays a bathochromic shift and simultaneous hypochromic effect with an isosbestic point at 370 nm, suggesting a shift between coexisting free and bound states. Similar results are observed with the intercalating agents adriamycin, ethidium bromide, and acridine. The fluorescence spectrum of coumestrol is quenched on exposure to DNA as are those of adriamycin and acridine. Coumestrol differs from the intercalators in that denatured DNA does not affect its UV spectrum or alter its relative fluorescence yield. Unlike classical intercalators, coumestrol has no influence on the thermal stability of calf thymus DNA. Preliminary electrophoretic analysis of DNA plasmid conformers indicates that coumestrol is incapable of significantly altering DNA superhelical density, in contrast to ethidium bromide. These initial physicochemical data provide evidence for the DNA base-estrogen electronic and/or hydrophobic interactions suggested by modeling studies, yet tend to rule out classical intercalation as an explanation for these phenomena.

Animals↗
PubMed1986

The stereochemical complementarity of DNA and reproductive steroid hormones correlates with biological activity.

Modeling studies revealed that progesterone, testosterone, and estradiol are stereochemically complementary to the cavity formed between base pairs in the DNA sequence, 5'-dTdG-3' X 5'-dCdA-3'. Each steroid aligned precisely with the topography of the cavity and formed 2 stereospecific hydrogen bonds linking phosphate oxygens on adjacent DNA strands. Hydrogen bonding donor-acceptor relationships were different for each hormone. The remarkable stereochemical specificity of the hormone-DNA complexes was demonstrated by the lack of complementarity of steroid enantiomers and steroid analogs having alternate ring systems and/or changes in the position of functional groups. Fit of molecules into DNA in the manner of the parent hormone correlated with biological activity. Antagonists also fit into the cavity but differed from agonists in their hydrogen bonding linkages to DNA and/or extended out of the cavity beyond the helix. Unlike flat intercalating agents which form stable complexes with DNA, wedge shaped steroids may thus be capable of forming reversible sequence-specific complexes with DNA. We conclude that the stereochemistry of DNA can be used to predict hormonal activity.

Animals↗
PubMed1985

Apparent stereochemical complementarity of estrogens and helical cavities between DNA base pairs: implications for the mechanism of action of steroids.

The shape of the space occupied by a model of the estrogenic steroid hormone estradiol-17 beta conforms closely to a helical cavity between neighboring base pairs in partially coiled B-DNA. The orientation of estradiol-17 beta when fitted into DNA allows stereochemically complementary hydrogen bonding of both the 3- and 17 beta-hydroxyl groups to phosphate oxygens of the deoxyribose-phosphate backbone on adjacent strands. Changes in the chirality (handedness) of the steroid skeleton or in the absolute stereochemistry of hydrogen bonding groups prevent formation of complementary fits in the DNA. Synthetic estrogens can also adopt conformations which are stereochemically complementary to the cavities between base pairs. The complementary relationships between active estrogens and nucleic acids may be related to constraints on the evolution of the structure and the biological function of steroids.

Base Composition↗
PubMed1983

Effect of CO2 induced pH changes on the response of isolated guinea pig tracheas to theophylline.

The effect of CO2 induced pH changes on the response of airway smooth muscle to theophylline was studied. Our data show that simulated respiratory acid-base disturbances (pH range 7.0 to 7.8) have no significant effect on the response of isolated guinea pig tracheal cylinders at basal tone to theophylline. On the other hand, tracheal cylinders precontracted with histamine showed a diminished sensitivity to theophylline at pH values above 7.40, and an enhanced sensitivity at pH values below 7.40.

Animals↗
PubMed1981

Are there structural analogies between amino acids and nucleic acids?

Space-filling molecular models have been used to examine structural analogies between amino acids and nucleic acids. The three-dimensional structures of amino acid R groups appear to be stereochemically related to cavities formed by removal of single bases in double helical nucleic acids. The common L amino acids may thus be complementary to their codons.

Adenine↗
PubMed1979

Effect of pH on the binding of theophylline to serum proteins.

The binding of theophylline to serum protein within the pH range of 7.0 to 7.8 was determined by equilibrium dialysis using serum from 8 healthy adult volunteers. The percentage of theophylline bound was independent of the total concentration of the drug, but was directly related to pH. Because changes in the free fraction of theophylline may alter the therapeutic response, toxic effects, and pharmacokinetics, any future studies of the pharmacology of theophylline should include assessment of the acid-base status of the patients and measurements of free as well as total theophylline concentrations.

Adult↗