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T Billington

Publications and source records attributed to T Billington.

31 records · Page 2Linked to original sources
PubMed1980

In vivo exchange of cholesteryl esters from low density lipoproteins to high density lipoproteins.

Labelled cholesteryl esters were injected within low density lipoproteins (LDL) in four subjects. In all experiments, cholesteryl esters transferred to HDL initially, at the rate of about 3% per hour. Very low density lipoprotein cholesteryl esters became labelled later, possibly by transfer from HDL. The simultaneous labelling of HDL free cholesterol by a second isotope (injected within mevalonic acid) showed that the rapid labelling of HDL cholesteryl esters from LDL was substantially faster than that from the esterification of HDL free cholesterol. While this process does not show net transfer of cholesteryl esters from LDL to HDL it indicates a pathway for equilibration of cholesteryl esters among plasma lipoproteins.

Aged↗
PubMed1979

In vivo transfer of cholesteryl esters from high density lipoproteins to very low density lipoproteins in man.

The fate of cholesteryl esters in high density lipoprotein (HDL) was studied to determine whether the transfer of esterified cholesterol from HDL to other plasma lipoproteins occurred to a significant extent in man. HDL cholesteryl ester, labelled in vitro with [3H] cholesterol, was injected into human subjects. Labelling of cholesteryl esters in very low density (VLDL) occurred rapidly and by 3 h, the esterified cholesterol in VLDL reached peak specific radioactivity. The removal rate of cholesteryl esters from HDL appeared to be exponential and of the order of 0.2/h; calculation of the apparent flux was about 150 mg/h which approximates reported values for total cholesterol esterification in human plasma in vivo. The rapid rate of labelling of VLDL from HDL suggests that the transfer of HDL cholesteryl esters to VLDL may represent a significant pathway for the disposal of HDL cholesterol.

Cholesterol↗
PubMed1979

Optimum concentration of dissolved oxygen for the survival of virulent Treponema pallidum under conditions of low oxidation-reduction potential.

A maintenance medium with a low oxidation-reduction (redox) potential, when gently bubbled with 5% oxygen in nitrogen or with air for various periods of time, gave a range of dissolved oxygen concentrations between 1.6 and 5.8 micrograms/l. Virulent Treponema pallidum (Nichols strain) inoculated into these media were assayed 24 and 48 hours later for motility and virulence and were compared with samples taken at zero time. Virulent T. pallidum survived best in the presence of 2.4 micrograms/l dissolved oxygen over a 48-hour period, which corresponded to a gaseous mixture of 3% oxygen in nitrogen. Higher concentrations of oxygen did not give significantly different results from anaerobic conditions over this period. Thus, until it can be grown in vitro, T. pallidum would appear to be a microaerophilic bacterium.

Anaerobiosis↗
PubMed1978

Studies on the brush border membrane on mouse duodenum: lipids.

Lipids were extracted from purified mouse duodenal brush border membranes. Lipid: protein ratios in different membrane preparations varied from 0.58 to 0.68. Both the chloroform and non-chloroform phases were quantitatively analysed for lipids. Chloroform extracts were composed of cholesterol, triglycerides and phospholipids. The major neutral lipid was cholesterol. Rechromatrography of the phospholipid spot showed sphingomyelin (7.9%), phosphatides of ethanolamine (61.7%), inositol (14.2%) and serine (16.2%). The average molar ratio of cholesterol to phospholipid was 1.39. Lipids in the non-chloroform phase were all glycosylated, being cerebrosides (69.3%), cerebroside sulphates (28.8%) and galgliosides (1.9%). Overal membrane lipid composition was neutral lipid 24%, phospholipid 33%, and glycolipid 43%.

Animals↗
PubMed1978

Glucose-binding membrane proteins.

To identify glucose-binding proteins amongst the polypeptides of the mouse duodenal brush border membrane, three types of experiments are reported. The first involved the introduction of labelled glucose and its analogue phlorizin into the lumen of separate groups of ligatured duodenal segments. Several proteins were shown to have bound both labelled species in situ by liquid scintillation counting of slices from polyacrylamide gels on which solubilised membrane protein had been electrophoretically separated. The second type of experiment was designed to determine the competitive nature of the binding of both labelled and cold phlorizin to proteins which had already bound glucose. Only three bands could competitively bind phlorizin. Finally, gels on which solubilised protein from in situ glucose-binding experiments had been run were placed in solutions containing labelled phlorizin. The binding of phlorizin to proteins in the same three bands as above suggested a confirmation of the conclusion that there were three membrane protein types which appeared to be involved in phlorizin-sensitive glucose-binding.

Animals↗
PubMed1978

Glycoproteins of the brush border membrane of mouse duodenum.

Qualitative and quantitative chemical analyses have been made of the carbohydrate and protein moieties of the glycoproteins in purified mouse duodenal brush border membranes. Solubilized membrane protein was electrophoresed on S.D.S.--polyacrylamide gels and glycoproteins were subsequently identified by periodate-Schiff staining. A parallel experiment showed that these glycoprotein bands also incorporated 14C counts from intraluminally-administered 14C-glucosamine. Positively-staining bands were collected from several identically run gels and subjected to digestion with pronase. The sugar and amino acid compositions of the digested glycoproteins were determined. Five of the membrane proteins appeared to be complexed with sugars, and further analyses showed that there were differences between the glycoproteins with respect to sialic acid, uronic acid, amino acids, amino sugar and monosaccharide contents.

Amino Acids↗
PubMed1978

The effect of solubilization on the properties of the insulin receptor of human placental membranes.

The insulin receptor for human placental membranes has been solubilized in Triton X-100 and its properties have been examined in detail. Binding of [125 I]iodoinsulin to the soluble receptor is markedly inhibited by increas-ng concentrations of Triton X-100, due to a fall in receptor affinity. In 0.02--0.10% Triton X-100, the soluble receptor exhibits all the essential characteristics of the intact or particulate receptor. These include strict specificity for insulin and its analogues, increase in steady state binding with decrease in temperature, a pH optimum at 7.8--8.0, and negatively cooperative site-site interactions. The initial association rate of [125 I]iodoinsulin and the soluble receptor is a direct function of temperature, but the level of steady-state binding is lower at higher temperatures due to a marked increase in dissociation rate. Scatchard binding plots are curvilinear and show a large increase in affinity at 4 C with no change in total binding capacity (R0); increased binding to the particulate placental membrane at 4 C is due chiefly to an increase in R3. Negative cooperatively in the soluble receptor has been confirmed by kinetic experiments; thus, the dissociation of [125I]iodoinsulin from the receptor in the presence of "infinite" dilution is accelerated in the presence of 10(-8) M unlabeled insulin. The apparent molecular weight of the placental receptor, determined by gel filtration on 6% agarose, is approximately 300,000. These studies show that the basic properties of the insulin receptor do not depend on it being an integral conponent of the cell membrane.

Female↗
PubMed1976

Studies on the brush border membrane of mouse duodenum. II. Membrane protein metabolism.

Mouse duodenal microvillus membrane protein metabolism was measured using radioactive labelling techniques. Labelled amino acids were introduced into the lumen of ligatured duodena. Following exposure to label, brush border membranes were isolated and analyzed. Experiments measuring the specific activity of protein labelled with a single amino acid revealed that total membrane protein appeared to turnover in about 14 hr. Protein in the mucosal homogenate had a faster turnover rate. Turnover rates of individual proteins were measured with single and dual isotope experiments. Membrane protein was solubilized with sodium dodecyl sulphate (SDS) buffer. Single isotope experiments showed that all polypeptides separated on SDS-gels were maximally labelled at 6 hr after injection. Bands did not incorporate label linearly. Rates of loss (degradation) of label from membrane proteins in the seventeen bands appeared to be related to the estimated molecular size of the proteins. Rates were highest for larger polypeptides. A double isotope technique, in which proteins were allowed to incorporate the same amino acid in two isotopic forms, delivered with a set time interval intervening, revealed that the ratios of the second label to the first in the SDS-separated polypeptides were highest for larger proteins and lowest for smaller polypeptides. Certain assumptions were outlined and the ratios taken as measures of turnover of proteins. Loss of label due to cell sloughing is discussed. A mixture of labelled amino acids (excluding leucine) was used to show that differences in leucine contents of different proteins was not an explanation for the variation in level of leucine radioactivity in different bands. For specific activity measurements throughout, protein in gels was quantitated with reference to the uptake of Coomassie stain. The use of this stain was validated by the finding that, at low protein concentration, the amount of stain taken up was proportional to the amount of bovine serum albumin or membrane protein loaded.

Animals↗
PubMed1976

Studies on the brush border membrane of mouse duodenum. III. Iodination of membrane proteins.

Microvillus membranes were iodinated from luminally administered lactoperoxidase, H2O2 and 125I before and after neuraminidase treatment. Membranes were isolated, solubilized in sodium dodecyl sulphate buffer and electrophoresed on gels. Gels were stained for protein, and then sliced for liquid scintillation counting. When membranes were not treated with neuraminidase, the nonpermeating iodination probe attached only to a band containing protein of 150,000 daltons approximate molecular weight. This size class of protein may reside on the luminal side of the brush border membrane as opposed to the serosol side. Qualifications of this statement are discussed with reference to the location of tyrosyl residues and to the possibilities of masking molecules. Membranes treated from the luminal side with neuraminidase to remove possibly masking carbohydrate and then iodinated, appeared to contain an additional protein of estimated molecular weight 220,000 daltons which was accessible to 125I. Thus, a 220,000 dalton protein may also be on the luminal side of the membrane. An explanation is attempted for the discrepancy between the very few proteins labelled and the many proteins involved in terminal digestion and transport which would all be expected to be available to luminally administered iodination probe. Membranes were isolated, exposed to iodination and then solubilized for electrophoresis. Nearly all proteins were labelled, which indicated that there is an asymmetric distribution of proteins in the plane of the membrane. The two smallest molecular weight polypeptides which were not iodinated were proposed to be so disposed in the membrane that they were inaccessible to the probe, from either side.

Animals↗
PubMed1975

Studies on the brush border membrane of the mouse duodenum. I. Membrane isolation and analysis of protein components.

Brush border membranes have been isolated from villus epithelial cells of the adult Swiss mouse duodenum. Preparations of these membranes are not contaminated by other organelles as judged from electron-micrographs of sectioned pellets of brush borders. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins from brush borders solubilized in Tris-sodium dodecyl sulfate buffer reveals a reproducible Coomassie Brilliant Blue pattern of 17 bands. By comparing the brush border protein band positions with those of standard proteins run concurrently on sodium dodecyl sulfate-polyacrylamide gel slabs it is estimated that the 17 brush border proteins and subunits have molecular weights ranging from over 250,000 to around 16,000. Periodate-fuchsin sulfite staining shows that the five more slowly migrating, high molecular weight proteins are glycoproteins. The two proteins of smallest molecular size react positively with Oil Red O but have very small amounts of lipophilic amino acid residues, which indicates that the lipid extractable from the gels in these areas is a contaminant and is not bound to the proteins.

Animals↗
PubMedDate not supplied

Effects of probucol on low density lipoprotein removal and high density lipoprotein synthesis.

The possible mechanisms of action of probucol on the metabolism of low density lipoprotein and of high density lipoprotein were studied in 5 hyperlipidaemic subjects. The kinetics of LDL-B protein and of HDL-AI protein were determined by 2-pool analysis of specific radioactivity-time curves after reinjection of 131I-labelled LDL and 125I-labelled HDL at the end of placebo and treatment periods. Probucol increased the fractional removal rate of LDL in 4, an action probably linked to increased bile acid excretion which occurred in all 5 subjects. Nevertheless, the plasma cholesterol concentration fell significantly in only 3. The synthesis of HDL-AI protein fell substantially and was probably responsible for the consistent reduction in plasma apo-AI levels. Thus, probucol appears to enhance LDL-B protein removal and bile acid excretion but inhibits AI protein formation; all these effects may be determined in the small intestine.

Adult↗