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Biomedical subjects

T D Madden

Publications and source records attributed to T D Madden.

45 records · Page 3Linked to original sources
PubMed1982

Stabilization of bilayer structure for unsaturated phosphatidylethanolamines by detergents.

The structural preferences of mixed lipid systems containing egg yolk or 18:1c/18:1c phosphatidylethanolamine and representative detergents (Triton X-100, deoxycholate, octylglucoside and lyso-phosphatidylcholine) have been examined. It is shown that all these detergents exhibit an ability to stabilize a bilayer organization for the phosphatidylethanolamine at detergent to phosphatidylethanolamine molar rations of 0.05 to 0.5, depending on the detergent and/or phosphatidylethanolamine species. These results are interpreted in terms of molecular shape, where the 'inverted cone' shape detergents combine in a complementary fashion with 'cone shaped' phosphatidylethanolamine to result in net bilayer structure.

Detergents↗
PubMed1981

The modulation of Ca2+-ATPase activity of sarcoplasmic reticulum by membrane cholesterol. The effect of enzyme coupling.

The Ca2+-ATPase activity of sarcoplasmic reticulum is relatively low (less than 2 I.U.) in vesicles where enzyme activity is geared to calcium accumulation. Modulation of membrane fluidity by enriching the membrane with cholesterol has no significant effect on enzyme activity. Collapsing the Ca2+ gradient with the calcium ionophore, A23187, unmasks the inhibitory effect of membrane cholesterol on enzyme activity.

Animals↗
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↗
PubMedDate not supplied

Current concepts in membrane protein reconstitution.

The reconstitution of integral proteins into artificial lipid vesicles is largely prompted by the complexity of most biological membranes and the inherent difficulty of studying individual components in situ. Ideally, therefore, the reconstituted system should consist of a single protein in a lipid matrix which mimics the native membrane in all but its diversity. While such an approach allows individual components of a complex system to be studied in isolation it should also be sufficiently versatile to permit the generation of increasingly sophisticated multicomponent models. From the considerable number of reconstitution techniques which have been developed I have tried in this review to identify those characteristics of a particular system which maximise both the information it can provide and its versatility.

Detergents↗
PubMedDate not supplied

The modulation of membrane fluidity by hydrogenation processes. IV. Homogenous catalysis of liposomes using a water-soluble catalyst.

A water-soluble homogeneous catalyst has been applied to the hydrogenation of the double bonds within phospholipid liposomes in water. When the catalyst is added to an aqueous system, containing liposomes of unsaturated phospholipids, it partitions between the water and the liposomes. The structure of the liposomes as indicated by electron microscopy is not affected at low concentrations of the catalyst. The permeability properties of the liposomes are also unaffected. In the presence of hydrogen gas the unsaturated bonds of the lipids are readily hydrogenated. Potential applications of water-soluble homogeneous catalysts using liposome systems are described.

Hydrogenation↗