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Biomedical subjects

D Chapman

Publications and source records attributed to D Chapman.

At least 235 records · Page 13Linked to original sources
PubMed1981

Hydrogenation of plasma lipoproteins by a water-soluble catalyst; its use as a structural probe.

Hydrogenation of double bonds of fatty acyl chains in the lipids of individual, intact plasma lipoproteins has been accomplished using a water-soluble, homogenous catalyst. Up to 40% of the double bonds can be hydrogenated. The pattern of hydrogenation is similar for each of the lipoprotein fractions; the phospholipids are most extensively hydrogenated but small amounts of cholesteryl ester and triacylglycerol are also hydrogenated. This results is consistent with a surface location of phospholipids and with the majority of the apolar lipids being in a hydrophobic inner core since the catalyst was shown not to be specific for an individual lipid class. It also suggests the some cholesteryl ester and triacylglycerol may be near the lipoprotein surface, accessible to the catalyst. If this is the case, it is speculated that the known exchange of these neutral lipids between the lipoprotein classes and their degradation by lipolytic enzymes may thus be facilitated.

Cholesterol Esters↗
PubMed1981

The significance of 1-131 scan dose in patients with thyroid cancer: determination of ablation: concise communication.

Twenty-four patients with differentiated thyroid cancer were studied with diagnostic I-131 neck chest scans after having undergone bilateral subtotal thyroidectomy and initial I-131 therapy with either 30- or 100-mCi doses. With an endogenous stimulation protocol, follow-up studies were performed with neck and chest scans using 2 and 10 mCi I-131. A 400% increase in sensitivity was found with a 10-mCi dose relative to a 2-mCi dose. Comparison with therapeutic doses of 30 and 100 mCi resulted in further increases in the detection of residual iodine-avid tissue. We conclude that a 2-mCi or lower dose of I-131 is inadequate in evaluating residual iodine-avid tissue visually in patients with thyroid cancer. The study does not answer the critical question of whether it is necessary to treat a patient presenting a negative 2-mCi but a positive 10-mCi scan. It may be appropriate to define ablation visually as well as clinically, with further studies directed toward determining a treatment rationale in this patient population.

Adenocarcinoma↗
PubMed1980

Protein rotation and chromophore orientation in reconstituted bacteriorhodopsin vesicles.

Bacteriorhodopsin has been reconstituted into lipid vesicles with dipalmitoyl and dimyristoyl phosphatidylcholine. Circular dichroism (CD) measurements show that the proteins are in a monomeric state above the main lipid phase transition temperature (Tc), 41 and 23 degrees C for dipalmitoyl and dimyristoyl phosphatidylcholine, respectively. Below Tc, the CD spectrum is the same as that found for the purple membrane. The latter result implies that the orientation of the chromophore at these temperatures is most likely the same as in the purple membrane (70 degrees +/- 5 degrees from the normal to the membrane plane). Transient dichroism measurements show that below Tc the proteins are immobile, while above this temperature protein rotation around an axis normal to the plane of the membrane is occurring. In addition, from the data the angle of the chromophore for the rotating proteins with respect to the rotational diffusion axis can be calculated. This angle is found to be 30 degrees +/- 3 degrees and 29 degrees +/- 4 degrees in dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine, respectively. This is considerably smaller than the value of 70 degrees +/- 5 degrees for the natural biomembrane. A reversible reorientation of the chromophore above and below the respective main Tc transition temperature could explain the change of angle observed provided that all the molecules rotate above Tc.

Bacteriorhodopsins↗
PubMed1980

Phospholipid polymers--synthesis and spectral characteristics.

A new approach has been developed for the study of model and natural biomembranes. This involves the cross-linking of diacetylene groups after ultraviolet irradiation. For the study of model biomembranes, pure phospholipids (phosphatidylcholines) have been synthesized containing diacetylene groups in each acyl chain. The physical properties of these lipids have been examined and the conditions under which they polymerise have been determined. Polymerisation occurs when the lipid is in a crystalline phase, either compressed in KBr, dispersed in water (liposomes) or deposited on a suitable support (multilayers). The resultant polymer contains a conjugated backbone and is coloured. The visible spectrum of the phospholipid polymer is sensitive to its environment. Preliminary experiments show that similar polymerisation can be induced in Acholeplasma laidlawii cells grown on diacetylenic fatty acid.

Acholeplasma laidlawii↗
PubMed1980

The formation of polymeric model biomembranes from diacetylenic fatty acids and phospholipids.

Diacetylenic fatty acid monolayers at the air/water interface and multilayers on suitable supports polymerise when exposed to ultraviolet radiation. It has been found that polymerisation still occurs when monolayers are diluted with cholesterol or gramicidin. The rigid, crystalline nature of the films formed makes them useful biomembrane models. Phospholipids made from the fatty acids were less reactive. Multilayers deposited on hydrophobic supports would polymerise but not monolayers on water.

Chemical Phenomena↗
PubMed1980

Protein-lipid interaction. Biophysical studies of (Ca2+ + Mg2+)-ATPase reconstituted systems.

Differential scanning calorimetry, fluorescence spectroscopy and freeze-fracture electron microscopy have been applied to a study of the reconstituted Ca2+-ATPase proteins from sarcoplasmic reticulum when they are incorporated into pure lipid/water systems. The results obtained with these techniques have been used to examine the effects of this intrinsic protein upon the surrounding lipid at temperatures above and below the main lipid solid-fluid phase transition temperature (Tc). 1. Above this Tc value, the freeze-fracture data show that the proteins are randomly distributed within the plane of the bilayer. The fluorescence data show that as the protein content in the bilayer increases, so does the 'microviscosity'. 2. Below Tc the proteins occur in high protein to lipid patches, separate from the remaining crystalline lipid. The fluorescence data indicate that at these temperatures the presence of the protein causes a decrease in microviscosity, whilst the calorimetric data indicate a decrease in enthalpy of the main lipid transition. 3. A premelting of the high protein to lipid patches formed by phase separation within the lipid bilayers is indicated by the calorimetric and fluorescence data. This observation is used to rationalise the 'anomalous' properties of the dipalmitoyl phosphatidylcholine-ATPase of exhibiting activity at temperatures well below the lipid phase transition at 41 degrees C.

Animals↗
PubMed1980

Bacteriorhodopsin, boundary lipid and protein conformers: a spin label study.

A spin label study, as a function of temperature, has been made with the bacteriorhodopsin membrane using a stearic acid spin label. The ESR spectra show a strong variation with temperature and the presence of isosbestic points. The spectra are interpreted as indicating the presence of a two-component system with an activation energy (approx. 14 kcal/mol) corresponding to a protein conformational change. This activation energy is similar to that deduced from recent flash photolysis studies. It is concluded that the spin label is sensitive to the temperature-dependent protein conformational change in this membrane system.

Bacterial Proteins↗
PubMed1980

Raman scattering in bilayers of saturated phosphatidylcholines. Experiment and theory.

Raman spectroscopy has been applied to a model biomembrane structure in order to obtain information about phospholipid hydrocarbon chain ordering. The intensity of the 1130-cm-1 Raman line obtained from a dipalmitoylphosphatidylcholine (DPPC) coarse aqueous dispersion has been measured as a function of temperature. The intensities of this line anther with the pretransition was observed. A theory of chain conformations as a function of temperature and rules for the assignment of Raman scattering intensities for this line have been constructed. Good agreement with the DPPC experimental data has been obtained. Predictions for the intensity of this line as a function of temperature from dimyristoyl- and distearoylphosphatidylcholine dispersions have also been made.

Lipid Bilayers↗
PubMed1980

The incorporation of cholesterol into inner mitochondrial membranes and its effect on lipid phase transition.

Incubations of rat liver inner mitochondrial membranes with liposomes prepared from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol resulted in a considerable enrichment of the cholesterol composition of these membranes. This enrichment is not accompanied by an alteration in the membrane phospholipid content or fatty acid composition. The exogenous cholesterol appears to be integrated into the membrane structure because it has effects consistent with the known properties of this sterol in other natural and artificial membrane systems. Differential scanning calorimetry on both intact membranes and extracted lipids showed that as the ratio of cholesterol to phospholipid was increased, the endotherm corresponding to the lipid phase transition was reduced. Freeze-fracture electron microscopy of the native membranes showed that intramembranous particles are randomly distributed above the phase transition temperature. Below this temperature large smooth areas, believed to correspond to lipid in the gel state from which proteins have been excluded, can be observed. In the presence of high concentrations of cholesterol the fracture faces observed below the lipid transition temperature show no regions of phase segregation, and observation consistent with previous studies using pure lipids where cholesterol was observed to prevent the lipid undergoing a cooperative phase transition. The results are discussed in terms of the observed low concentrations of cholesterol in normal liver inner mitochondrial membranes and the distribution of cholesterol within the liver cells.

Animals↗
PubMed1980

Difference infrared spectroscopy of aqueous model and biological membranes using an infrared data station.

A Perkin-Elmer infrared Data Station associated with a simple IR spectrometer (model 298) is shown to give excellent results with aqueous model and biomembrane systems. Examples are presented of difference spectra obtained with lipid--water systems, reconstituted lipid--protein systems and a natural biomembrane. The spectra of the lipid after water subtraction and of the intrinsic protein after lipid subtraction from a model reconstituted Ca2+-ATPase membrane system are shown. The potential for studying intrinsic protein conformations is emphasised.

Animals↗
PubMed1980

Studies of liposome interactions with rat thymocytes.

1. The consequences of incubating liposomes with rat thymocytes have been studied using liposomes of dipalmitolyphosphatidylcholine and cholesterol or dipalmitoylphosphatidylcholine only. 2. Dipalmitoylphosphatidylcholine-cholesterol liposomes do not bind to the cells can be removed by washing. An increase in cellular cholesterol is observed. However dipalmitoylphosphatidylcholine liposomes bind rapidly to the cells and cannot be removed by repeated washing. Cholesterol is removed from the cells. 3. There are small changes in intracellular cations in the cholesterol-enriched cells, but no transport studies have been made. Cells depleted of cholesterol lose K+ with little change in intracellular Na+. Na+ influx is increased. The majority of this increase appears to be ouabain-sensitive, indicating in pump-mediated Na+ influx. K+ influx is reduced. 4. The significance of these results is discussed.

Animals↗