Search PubMed⌕ Search

Biomedical subjects

J C Osborne

Publications and source records attributed to J C Osborne.

At least 73 records · Page 4Linked to original sources
PubMed1980

Peroxidase activity in the rat Zymbal gland and its possible role in the metabolic activation of aminostilbenes in the target tissue.

Peroxidase (EC 1.11.1.7) activity is detected in the rat Zymbal gland, which is the target organ of trans-4-dimethylaminostilbene (trans-DAS) carcinogenicity. Measurements of peroxidase activity in ovariectomized rats show that the enzyme activity is lowered in the uterus and Zymbal gland by trans-DAS treatment and in the lungs by diethylstilboestrol (DES) treatment. In an in vitro system containing horseradish peroxidase (HRP), hydrogen peroxide and calf-thymus DNA, irreversible binding of the 3H-labelled trans-DAS metabolites 3-hydroxy-, 4'-hydroxy-, and N-hydroxy-4-acetylaminostilbene to DNA is observed. The peroxidase activity in the Zymbal gland together with the HRP-catalyzed oxidation of trans-DAS metabolites suggest a possible role for peroxidase in the organ-specific metabolic activation of trans-DAS.

Animals↗
PubMed1978

Effect of pressure and ionic strength on the self-association of Apo-A-I from the human high density lipoprotein complex.

The self-association of apo-A-I isolated from the human high density lipoprotein complex has been investigated by gel permeation chromatography and sedimentation equilibrium. The apparent weight average molecular weight (MWapp) versus Apo-A-I concentration profile was found to be sensitive to ionic strength and pressure; MWapp increased with increasing ionic strength and decreasing rotor speed. The data were consistent with a monomer-dimer-tetrameroctamer association shceme over all conditions investigated if a change in the partial specific volume of apo-A-I upon association of 5.5 x 10(-2) ml/g is postulated.

Apolipoproteins↗
PubMed1978

Interaction of human chorionic gonadotropin with membrane components of rat testes.

Previous studies demonstrating that gangliosides interacted with thyrotropin and human chorionic gonadotropin (hCG) suggested that gangliosides participate in the transduction of the hormonal message across the target cell membrane. As a continuation of these investigations, we examined the effects of down-regulation of hCG receptors on the interaction of hCG with rat testis membrane components. Rat testes contained a complex ganglioside pattern that did not appear to change qualitatively or quantitatively after the injection of hCG into the animals, although testis membranes from hCG-treated rats lost their capacity to bind (125)I-labeled hCG ((125)I-hCG). Gangliosides extracted from the testes of control and treated animals were equally effective inhibitors of (125)I-hCG binding to testis membranes. However, inhibition of binding was observed only under conditions (pH 6.0, low ionic strength) such that unlabeled hCG (>2500-fold excess) did not block (125)I-hCG binding, and (125)I-hCG bound similarly to testis membranes from control and treated rats. Under conditions such that hCG binding was specific (blocked by 250-fold excess of unlabeled hCG), testis gangliosides were noninhibitory. Liposomes containing gangliosides from the testes of control or hCG-treated rats bound similar small amounts of (125)I-hCG. These same liposomes bound 50 and 1000 times more thyrotropin and cholera toxin, respectively, than hCG. Oligosaccharides derived from gangliosides did not inhibit (125)I-hCG binding to testis membranes nor did they alter the fluorescence of hCG conjugated with fluorescent probes, whereas the gangliosides themselves were inhibitory and enhanced the fluorescence intensity of the hCG derivatives. Exposure of testis membranes from hCG-treated rats to 4 M MgCl(2), which displaces bound hCG [Chen, Y.-D. I. & Payne, A. H. (1977) Biochem. Biophys. Res. Commun. 74, 1589-1596], did not restore their ability to bind (125)I-hCG. When membranes were solubilized with Triton X-100, a solubilized receptor was detected from testis membranes of control but not hCG-treated rats. These findings and the absence of demonstrable changes in the composition or quantity of rat testis gangliosides when hCG receptors are down-regulated suggest that gangliosides do not represent the primary binding determinants of hCG receptors.

Animals↗
PubMed1977

Self-association of apo-C-I from the human high density lipoprotein complex.

The molecular properties of apo-C-I, isolated from the human high density lipoprotein complex, have been evaluated as a function of pH, solvent composition, and protein concentration by sedimentation equilibrium and circular dichroic measurements. This protein self-associates in aqueous solution at neutral pH with concomitant changes in secondary structure. In contrast, in the acid pH range, apo-C-I is monomeric and its ellipticity is independent of protein concentration. The results are discussed in terms of the interpretation of experiments where changes in the physical properties of apolipoproteins have been used to monitor ligand binding and lipid-apolipoprotein recombination.

Apolipoproteins↗
PubMed1977

Effect of gangliosides and substrate analogues on the hydrolysis of nicotinamide adenine dinucleotide by choleragen.

Choleragen and its A protomer catalyzed the hydrolysis of NAD to ADP-ribose and nicotinamide. NADase activity was inhibited by gangliosides GM1 (galactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylglucosylceramide), GM2 (N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylglucosylceramide), GM3 (N-acetylneuraminyl-galactosylglucosylceramide), and GD1a (N-acetylneuraminylgalactosyl-N-acetylgalactosaminyl-E1N-acetylneuraminyl]-galactosylglucosylceramide). These gangliosides also increased the intensity of the tryptophanyl fluorescence of the isolated A protomer (lambda max = 328 nm). GM1 but not GM2, GM3, and GD1a caused a "blue shift" in the fluorescence spectrum of the B protomer. These results are consistent with other evidence that the specificity of GM1 as the choleragen receptor resides in its carbohydrate moiety. The NADase activity of choleragen was similar to that of diphtheria toxin previously described [J. Kandel, R. J. Collier & D. W. Chung (1974) J. Biol. Chem. 249, 2088-2097]. As with diphtheria toxin, analogues of NAD were inhibitory, adenine being the most effective. Significant inhibition was also noted with adenosine, AMP, ADP-ribose, nicotinamide, nicotinamide mononucleotide, and NADP. NADP was hydrolyzed only slowly by choleragen. In the NADase reaction catalyzed by diphtheria toxin, water serves as an acceptor for the ADP-ribose moiety of NAD in lieu of the natural acceptor molecule, which is elongation factor II (Kandel et al., 1974). It seems probable that the natural protein acceptor for ADP-ribose in the reaction catalyzed by choleragen is adenylate cyclase or a protein component of a cyclase complex that regulates enzymatic activity.

Adenine↗
PubMed1977

A congenital pulmonary anomaly (hamartoma) in a seven-month-old bovine fetus.

A case of an unusually large congenital pulmonary malformation (hamartoma) in a seven-month-old aborted Holstein fetus is reported. This was the dam's sixth gestation; the previous five had terminated in November or early December with delivery of a normal, live calf. Abortion was spontaneous without prior clinical signs noted by the herdsman. The condition of the aborted fetus indicated abortion followed closely intrauterine fetal death, which probably resulted from vascular insufficiency owing to crowding in the fetal thorax by the massive pulmonary malformation.

Abortion, Veterinary↗
PubMed1975

The self-association of the reduced ApoA-II apoprotein from the human high density lipoprotein complex.

The molecular properties of the single linear chain form of human apoA-II, i.e., Cm apoA-II, have been evaluated by circular dichroism, polarization of fluorescence, difference absorption, and sedimentation equilibrium. The self-association of Cm apoA-II to a dimer resembles closely that of apoA-II though the free energy change is somewhat smaller. The dimerization of Cm apoA-II is accompanied by major changes in secondary and tertiary structure. The apoA-II molecule, therefore, represents a molecular association where the intramolecular structure is strongly dependent on the quaternary structure.

Apoproteins↗