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Biomedical subjects

M C Phillips

Publications and source records attributed to M C Phillips.

At least 145 records · Page 8Linked to original sources
PubMed1981

Phase behavior of ether lipids from Clostridium butyricum.

Ether lipids have been isolated from the phospholipid fraction of Clostridium butyricum IFO 3852 cells which had been grown in media devoid of biotin with added elaidic acid or oleic acid. The plasmalogen form of phosphatidylethanolamine (plasmenylethanolamine) from elaidate-grown cells was highly enriched with 18:1 in both the alk-1-enyl and acyl chains. A transition from the gel to liquid-crystalline state, with a peak maximum (Tm) at 33 degrees C and enthalpy delta H = 5.7 kcal/mol, was observed by differential scanning calorimetry. With the fluorescent probes cis- and trans-parinaric acids, transitions were observed at 33 degrees C on heating and at 29 degrees C on cooling. These transition temperatures are 5-6 degrees C lower than those reported for the corresponding diacyl lipid, dielaidoylphosphatidylethanolamine. A similar study of the phase behavior of both the elaidate-enriched and oleate-enriched glycerol acetal derivative of plasmenylethanolamine from C. butyricum revealed a large hysteresis of 12.5-16 degrees C. Hysteresis in the polar head group motion was also observed by 31P nuclear magnetic resonance. The elaidate-enriched lipid, which melted between 28 and 33 degrees C, appears to undergo supercooling prior to the transition to the gel state at about 18-13 degrees C, depending on the scanning rate. The formation of a more ordered gel state relative to plasmenylethanolamine was indicated by a 2-fold increase in delta H. Electron microscopy revealed a marked reorganization from typical multilamellar liposomes above Tm to large needle-like structures below Tm. The oleate-enriched glycerol acetal lipid formed the gel phase at -4 degrees C, which is 10 degrees C above the transition temperature reported for dioleoylphosphatidylethanolamine. Stabilization of oleate-enriched glycerol acetal lipid bilayers may result from hydrogen bonding between polar head groups. The relationship of the phase behavior of the ether lipids to the lipid composition and phase behavior of C. butyricum membranes is discussed.

Calorimetry, Differential Scanning↗
PubMed1979

The physical properties of an effective lung surfactant.

It is suggested that the phospholipids at the alveolar/air interface exhibit both thermodynamic (equilibrium) and kinetic forces during the course of a respiratory cycle. The alveolae are kept open at full expiration by a residue of nearly pure dipalmitoyl phosphatidylcholine which is condensed and therefore, incompressible at 37 degrees C.

Chemical Phenomena↗
PubMed1976

Interaction of apoprotein from porcine high-density lipoprotein with dimyristoly lecithin. 2. Nature of lipid-protein interaction.

The detailed molecular structure of the complex formed by the apoprotein from porcine high density lipoprotein and dimyristoly phosphatidylcholine (lecithin) has been investigated by a range of physical techniques. The complex, an oblate ellipsoid with major axis 11.0 nm and minor axis 5.5 nm (see the accompanying paper), is comprised of a section of lecithin bilayer with apoprotein at the surface. The main site of interaction between protein and lipid is in the lipid glycerophosphorylcholine group region; as with native high density lipoprotein the surface of the particle consists of a mosaic of lecithin polar groups and protein. The formation of this mosaic reduces the cooperativity of the lecithin chain motions and changes the curvature of the lipid-water interface, as compared to a bilayer. Otherwise, there are no major changes in lecithin motions indicating that no strong binding of lipid to protein occurs. The interaction involves the intercalation of amphipathic, 60% alpha-helical, apoprotein molecules among the lecithin molecules so that the protein residues at the lipid-water interface. The apoprotein has a high affinity for the lipid-water interface but specific lipid-protein interactions are not involved.

Amino Acid Sequence↗
PubMed1976

Ion-binding to phospholipids. Interaction of calcium with phosphatidylserine.

The binding of Ca2+ to monolayers and bilayers of phosphatidylserine has been investigated as a function of pH, ionic strength (NaCl concentration) and Ca2+ concentration using surface and colloid chemical techniques. The molar ratio of lipid to bound calcium decreases to 2 as the Ca2+ concentration is increased to about 0.1 mM. At [Ca2+] greater than 0.1 mM a 1:1 complex is formed. The apparent binding constant Ka ranges from about approximately 10(6) - 10(4) l/mol depending on the Ca2+ concentration. After allowing for electrostatic effects and neighbour group interactions, the intrinsic binding constant Ki of the phosphorylserine polar group at pH 7 (I = 0.01 M), where it carries a net negative charge of one, is approximately 10(4) l/mol; consistent values for Ki were obtained using several independent approaches. Ka for Ca2+ binding decreases with increasing NaCl concentration because the monovalent cations compete with Ca2+ for the same binding site. Na+ and K+ are equally effective in displacing 45Ca2+ adsorbed to monolayers of phosphatidylserine, both with respect to the kinetics and the equilibrium of the displacement. Ka for the reaction between phosphatidylserine and monovalent cations is about 10(3)-fold smaller than that of Ca2+. An investigation of the binding of Mn2+ to phosphatidylserine by both surface chemical and nuclear magnetic resonance methods shows that this cation has a similar binding constant to that of Ca2+. The Ca2+-binding capabilities of monolayers containing only carboxyl groups (i.e. arachidic acid) and phosphodiester groups (i.e. dicetyl phosphate) have also been determined; the apparent pK for the - COOH group in monolayers is larger than or equal to 9 and that for the phosphodiester group is less than 4. Since these groups do not retain the same pK values when they are in close proximity in the phosphorylserine group, the relative contributions of the two groups to the binding of Ca2+ to phosphatidylserine is not obvious.

Binding Sites↗
PubMed1975

Differences in the interaction of inorganic and organic (hydrophobic) cations with phosphatidylserine membranes.

The interaction of phosphatidylserine dispersions with "hydrophobic", organic cations (acetylcholine, tetraethylammonium ion) is compared with that of simple inorganic cations (Na+, Ca2+); differences in the hydration properties of the two classes of ions exist in the bulk phase as evident from spin-lattice relaxation time T1 measurements. It is shown that the reaction products (cation-phospholipid) differ markedly in their physicochemical behaviour. With increasing concentration both classes of ions reduce the zota-potential of phosphatidylserine surfaces, the monovalent inorganic cations being only slightly more effective than the hydrophobic cations. Inorganic cations cause precipitation of the lipid once the surface charge of the bilayer is reduced to a certain threshold value. This is not the case with the organic cations. The difference is probably associated with the different hydration properties of the resulting complexes. Thus binding of Ca2+ causes displacement of water of hydration and formation of an anhydrous, hydrophobic calcium-phosphatidylserine complex which is insoluble in water, whereas the product of binding of the organic cations is hydrated, hydrophilic and water soluble. The above findings are consistent with NMR results which show that the phosphodiester group is involved in the binding of both classes of cations as well as being the site of the primary hydration shell. Besides affecting interbilayer membrane interactions such as those involved in cell adhesion and membrane fusion, the binding of both classes of cation can affect the molecular packing within a bilayer.

Acetylcholine↗
PubMed1975

A comparison of the interfacial interactions of the apoprotein from high density lipoprotein and beta-casein with phospholipids.

The conformations adopted by beta-casein and the total apoprotein from serum high density lipoprotein when spread at the air-water interface are compared; the monolayer data are consistent with the apoprotein being alpha-helical and the beta-casein being disordered with segments distributed in loops and trains. The penetration of these hydrophobic proteins into phosphatidylcholine monolayers in different physical states was investigated. More protein can penetrate into monolayers when they are in the liquid-expanded state; for penetration at constant total surface area the lateral compressibility of the lipid is an important factor. The charge and conformation of the polar group of the phospholipid does not have a major influence on the interaction. The mixed films of lipid and protein have a mosaic structure; probably the beta-casein is in a compressed state whereas the apoprotein is extended as alpha-helices in the plane of the interface. The chain-length depedences of the interaction of the apoprotein with phosphatidylcholine monolayers and bilayers are different; when the apoprotein binds to bilayers of shorter-chain phosphatidylcholines it alters the shape of the lipid-water interface whereas with monolayers the interface remains planar throughout.

Apoproteins↗
PubMed1975

Ion-binding to phospholipids. Interaction of calcium and lanthanide ions with phosphatidylcholine (lecithin).

Surface chemical and nuclear magnetic resonance (NMR) techniques have been used to study the interaction of Ca2+ and lanthanides with lecithins. With both methods positive reactions were detected at metal concentrations greater than 0.1 mM. 1H and 31P high-resolution NMR spectra obtained with single bilayer vesicles of lecithin were invariant up to Ca2+ concentrations of 0.1 M indicating that there is only a loose association between Ca2+ and the phospholipid. The weak interaction between Ca2+ and lecithin is confirmed by both surface chemical and NMR techniques showing that the packing of egg lecithin molecules present in bilayers does not change up to Ca2+ concentrations of about 0.1 M. The packing was also independent of pH between 1--10. Contradictory results have been reported in the literature concerning the question of Ca2+ binding to lecithins. The conflicting results are shown to have arisen from differences in the experimental conditions and differences in the sensitivity of the physical methods used by various authors to study Ca2+ -lecithin interactions. An estimate of the strength of binding and molecular details of the interaction were derived using paramagnetic lanthanides as isomorphous replacements for Ca2+. From the changes in chemical shifts induced in the presence of lanthanides an apparent binding constant KA approximately 30 l/mol was calculated at lanthanide concentrations greater than 10 mM. Using surface chemical methods it was shown that this KA is up to 10 times larger than that for Ca2+ binding. The complete assignment of the 1H NMR spectrum of lecithin, including the resonances from the relatively immobilized glycerol group, was determined to derive molecular details of the cation-lecithin interaction. From spin-lattice relaxation-time measurements and line broadening in the presence of GdCl3 it is concluded that the cations are bound to the phosphate group and that this is the only binding site. The absolute proton shifts induced by paramagnetic lanthanides depended on the nature of the ion, but the shift ratios standardised to the shift of the O3POCH2 (choline) signal were invariant throughout the lanthanide series indicating that the shifts are purely pseudocontact. In contrast the 31P shifts were found to contain significant contact contributions. These findings are consistent with a weak interaction and with the phosphate group being the binding site. The absolute shifts but not the shift ratios depended on the anion present indicating that the cation binding may be accompanied by binding of anions. Contrary to negatively charged phospholipids the interaction of lanthanides with lecithins was enhanced as the ionic strength was increased by adding NaCl. This was explained in terms of steric hindrance due to the extended conformation of the lecithin polar group.

Binding Sites↗
PubMed1975

Monolayer characteristics of some glycolipids at the air-water interface.

Surface pressure and surface potential versus molecular area data have been obtained for some galactosyldiglycerides and some galactosphingolipids at the air-water interface. The physical states of galactolipid monolayers (and bilayers) parallel those of the phospholipids. The molecular packing of the monolayers is determined primarily by the interactions between the hydrocarbon chains and chain melting causes the transition from condensed to expanded monolayer. Thus the long saturated chain cerebrosides from myelin have high chain-melting temperatures and form condensed monolayers with the chains in a quasi-crystalline array. The galactosyldiglycerides from chloroplast membranes contain polyunsaturate chains and form liquid-expanded monolayers. The surface potentials of monolayers of neutral galactosyldiglycerides are similar to those of equivalent lecithins; the contributions of the hydrated galactose and phosphorylcholine moieties to the surface potential are approximately equal. The various galactosphingolipid monolayers studied have quite different surface potentials; this indicates that relatively small variations in molecular structure which do not lead to appreciable changes in the average packing density can cause large changes in surface potential.

Diglycerides↗
PubMed1975

Milk and its role in the American diet.

A decline in milk consumption is postulated as a possible factor contributing to poor nutritional status. Certain common prejudices against milk may, rightly or wrongly, act as barriers to its consumption and, therefore, to its nutritional contributions. Beliefs such as "adults don't need milk;" "raw milk is better than pasteurized milk;" "nonwhite people shouldn't drink milk;" "saturated fat and cholesterol 'cause' heart disease;" "cows are ecologically unsound;" and "nutrition doesn't sell milk" can be counteracted in light of current scientific knowledge and information. It is reaffirmed that milk, in moderation, is a desirable inclusion in most people's diets.

Adolescent↗