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Biomedical subjects

I R Miller

Publications and source records attributed to I R Miller.

At least 37 records · Page 2Linked to original sources
PubMed1986

An infrared spectroscopic study of metastable and stable forms of hydrated cerebroside bilayers.

Fourier transform infrared spectroscopy has been used to study the stable and metastable forms of a range of cerebrosides in aqueous systems. The spectra provide evidence for different degrees of inter- and intra-molecular hydrogen bonding, involving principally the amide group, in these different states. A comparison has been made with the spectra of a cerebroside containing an alpha-hydroxyl group in the fatty acyl chain. This cerebroside does not show metastability and its hydrogen bonding characteristics are shown to be different.

Cerebrosides↗
PubMed1986

Circular dichroism spectra of aqueous dispersions of sphingolipids.

The circular dichroism (CD) spectra of a number of sphingolipids dispersed in water have been studied. The lipids include cerebrosides such as palmitoyl cerebroside, glucocerebroside from the spleen of Gaucher patients, bovine brain galactocerebrosides type I and type II, (BCI and BCII, respectively) and also sphingomyelins such as egg sphingomyelin and bovine brain sphingomyelin. Changes in the CD spectra of the lipids which occur upon heating and cooling and the effects of cholesterol, phosphatidylcholine and the opiate leucine enkephalin were studied.

Animals↗
PubMed1985

Thermotropic properties of bipolar lipids of Sulfolobus solfataricus and of their mixtures with dipalmitoylphosphatidylcholine.

The thermotropic properties of the bipolar lipids, glycerol dialkylglycerol tetraether (GDGT) and glycerol dialkylnonitol tetraether (GDNT), were determined at different degrees of hydration and in mixtures with dipalmitoylphosphatidylcholine (DPPC). The number of water molecules rendered unfreezable by the GDNT molecule is 10+/-1.5 and that by the GDGT molecule 2.8+/-0.7 or about 1.1-1.5 H2O molecules per OH group. Binding of water molecules causes randomization of the two polar heads from the oriented form prevailing in the dry state. The hydration seems to be a cooperative process extending over a whole lipid domain. DPPC added in small amounts to GDNT interacts preferentially with the nonitol halves of the molecules separating them from the glycerol half molecules. In the cooperative interaction domain each DPPC molecule is surrounded by up to six GDNT molecules. Cooperative domains formed during the interaction of DPPC with GDGT are less pronounced. In both cases they affect the thermotropic properties of the system.

Journal Article↗
PubMed1982

Calorimetric studies on various gangliosides and ganglioside-lipid interactions.

Differential scanning calorimetry was used to investigate the thermotropic behaviour of various gangliosides differing in size and in the net negative charge. It was found that the number and the position of the negative charges in the headgroup region influence strongly the phase transition profiles. Interaction of GM1 ganglioside with egg phosphatidylcholine or cholesterol was also investigated. GM1 is completely miscible with egg phosphatidylcholine, giving only one transition peak at all ratios of the two components, implying that when gangliosides are in a more fluid lipid environment in biological membranes they will be randomly distributed. Interaction with cholesterol decreases the enthalpy of melting of the ganglioside. The decrease in enthalpy reaches a plateau at about 30 mol% cholesterol, suggesting a lower affinity of cholesterol for gangliosides than for sphingomyelin.

Animals↗
PubMed1982

Compositional aspects of lipid hydration.

The effect of various lipids such as cerebrosides, gangliosides and dipalmitoyl lecithin (DPPC) on the lowering of the melting temperature of water, was determined by differential scanning calorimetry (DSC). The lowering of the melting temperature, and the number of water molecules per lipid molecule which apparently do not undergo melting, increase with the increase of the size and charge of the polar group and with the unsaturation of the hydrocarbon chains. Freezing curves show supercooling to about -20 degrees C. It was found that the number of apparently unfreezable water molecules is about four for glucocerebroside from Gaucher's spleen and about eight or nine for galactocerebroside from bovine brain. In gangliosides from bovine brain the following number of water molecules/lipid molecule are apparently unfreezable: 22-30 in GM1, 33-40 in GD1a + GD1b while a fraction of gangliosides containing 75% GQ1b and 25% GT1b affects up to 60 molecules of water/molecule of lipid. A zwitterionic DPPC molecule removes apparently six to seven water molecules from freezing. There is no indication that the apparently unfreezable water molecules are in a distinct state. It is suggested that they freeze at very low temperatures producing a flat tail preceding the transition peak which cannot be discerned from the base line.

Animals↗
PubMed1980

Transfer of insulin receptors and of glucose transport-inducing proteins onto phospholipid vesicles.

Insulin receptors and glucose transport-inducing proteins have been extracted from rat liver membranes onto positively charged lipid bilayer vesicles. The extraction was carried out during the incubation of the vesicles with lipid vesicles caused an overall enhancement of specific insulin binding and of glucose transport inducement. The latter has been inferred from the oxidation rate of transported glucose through a spherical bilayer membrane entrapping the oxidizing glucose oxidase. Glucose transport is not enhanced by insulin binding, indicating that the two functions baecome dissociated when the proteins are transferred from the plasma membrane onto the bilayer vesicles.

Animals↗
PubMed1980

Interaction of prothrombin and its fragments with monolayers containing phosphatidylserine. 1. Binding of prothrombin and its fragment I to phosphatidylserine-containing monolayers.

The adsorption isotherms of prothrombin and its fragment I on phosphatidylserine monolayers and on mixed monolayers of phosphatidylcholine and phosphatidylserine were determined by measuring surface radioactivity emanating from the tritium-labeled absorbed proteins at 0.1 N NaCl and between 0 and 10 mM Ca2+. The proteins were absorbed from very dilute solutions, about 10 times more than in previous investigations on bilayer vesicles. The binding constants as obtained from the Scatchard plots were between 3 X 10(6) and 3 X 10(8) mol/L, depending on the experimental conditions. These values are between 2 and 50 times larger, respectively, than the binding constants obtained on bilayer vesicles. Prothrombin absorbs appreciably also in the absence of Ca2+. The significance of these results is discussed.

Adsorption↗
PubMed1980

Perturbations of membrane structure by optical probes: II. Differential scanning calorimetry of dipalmitoyllecithin and its analogs interacting with Merocyanine 540.

Differential scanning calorimetry of multilamellar liposomes, interacting with the optical probe Merocyanine 540, yields quantitative information about perturbances of the bilayer structure induced by this dye. At low dye: lipid ratios, the dye perturbs primarily its own microenvironment, which is laterally separated from the unmodified lipid domain and exhibits modified thermotropic properties. A further increase in the dye concentration results in a perturbance of the whole lipid bilayer. The degree of perturbance is sensitive to structural modifications in the head-group region of the lipids. It is concluded that Merocyanine 540 reports in every case, even at infinite dilution, on localized events originating from a perturbed microenvironment.

Benzoxazoles↗
PubMed1978

Differential scanning calorimetry of dipalmitoyl phosphatidylcholine analogues and of their interaction products with basic polypeptides.

The thermotropic behaviour of dipalmitoyl phosphatidylcholine analogues with a varying number (n) of CH2 groups between the phosphate and the quaternary ammonium has been investigated. The temperature (Tm) and the enthalpy (deltaH) of the phase transition are non-monotonous functions of the number of CH2 groups. Tm oscillates between 40 and 45 degrees C and deltaH between 7 and 13 kcal/mol for a variation of n between 2 and 11. It is concluded that the hydrocarbon chains in the head groups do not penetrate the hydrocarbon region and do not contribute directly to the melting of the acyl chains. It is suggested that their length may affect the critical balance between the attractive and the repulsive forces within the bidimensional lattice of the head groups. Copolypeptides of lysine with phenylalanine do not appreciably affect the Tm but have a pronounced effect on deltaH of the lipid phase transition, which depends strongly on the ratio of the two amino acids in the polypeptide. The effect of copolypeptide of any defined composition on deltaH is also a non-monotonous function of the number of CH2 groups in the phosphatidylcholine head group, but it does not parallel completely the oscilations in the Tm and deltaH of the pure lipids.

Calorimetry, Differential Scanning↗
PubMed1978

Differential scanning calorimetry of rat liver mitochondria.

Differential scanning calorimetry was employed for studying rat liver mitochondria and extracted mitochondrial lipids. Endothermic transition in the range 15--40 degrees C was detected for the whole mitochondria and between 10--20 degrees C for the extracted lipids.

Animals↗
PubMed1978

Effect of polymyxin B on the structure and the stability of lipid layers.

Polymyxin B (PX) does not penetrate phospholipid monolayers and bilayers at low field strength across the lipid layers. The degree of penetration of PX is evaluated from its effect on the capacitance of the monolayers and on the conductance of the bilayers. PX added to one side of a bilayer causes its destabilization, it also enhances destabilization of lipid monolayers at positive electric fields across the surface layer in the direction of the adsorbed PX. PX lowers very little the fluorescence polarization of 1,6-diphenyl 1,3,5 hexatriene embedded in phospholipid vesicles. It is suggested that the penetration mechanism of PX into gram-negative bacteria is based on transient local breakdown of the plasma membrane.

Adsorption↗
PubMed1976

Enzymic activity at interfaces. II. Enzymic activity of microsomal nuclease and bovine pancreatic ribonuclease at the air/water interface.

The adsorption isotherms and the spreading tendency of microsomal nuclease (nucleate 3'-oligonucleotidohydrolase, EC 3.1.4.7) and bovine pancreatic ribonuclease (ribonucleate 3'-pyrimidino-oligonucleotidohydrolase, EC 3.1.4.22) in the presence of isopropyl alcohol as spreading agent have been determined using enzymes radioactively labelled by acetylation. In parallel, the concentration-surface pressure relations have been established. The enzymic activity of microsomal nuclease spread from isopropyl alcohol containing aqueous solutions was only a few percent of its activity in bulk, while the activity of the adsorbed enzyme was only slightly reduced. Adsorbed monolayers of RNAase were almost inactivated, while the spread monolayers in the presence of isopropyl alcohol became reactivated after exposure to the substrate for several hours. The exposure time for the reactivation decreases with increasing surface concentration.

Air↗