Studies on phospholipid mono- and bilayers.
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Cell Membrane↗
Biomedical subjects
R A Demel
Publications and source records attributed to R A Demel.
Interaction between lecithins and cholesterol at the air-water and oil-water interfaces.
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Air↗
Further studies on the hemolytic action of filipin and derivatives.
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Alkenes↗
Substitution of Ser61----Gly61 in human apolipoprotein C-II does not alter its activation of lipoprotein lipase.
Lipoprotein lipase (LpL) activity is enhanced by apolipoprotein C-II (apoC-II), a 79 amino acid residue peptide. The minimal apoC-II sequence required for activation of LpL resides between residues 56-79. To determine the possible role of an acyl-apoC-II intermediate involving Ser61 in enzyme catalysis, a synthetic peptide of apoC-II containing residues 56-79 was synthesized and compared to the corresponding peptide with serine at position 61 being substituted with glycine. With two different LpL assay systems, both peptides enhanced enzyme activity. Since glycine does not contain a hydroxyl group, these results rule out the possibility that an acyl-apoC-II intermediate with Ser61 is required for enzyme activation.
Amino Acids↗
Monolayer characteristics and thermal behaviour of phosphatidic acids.
The monolayer and thermal behaviour of different phosphatidic acids are presented. At neutral pH and 22 degrees C dilauroylphosphatidic acid and unsaturated phosphatidic acids form liquid-expanded monolayers, while dipalmitoyl- and distearoylphosphatidic acid form condensed monolayers. Dimyristoylphosphatidic acid undergoes a transition from the liquid-expanded to the condensed state. With long-chain saturated and unsaturated phosphatidic acids little change in molecular area is observed between pH 2 and 7. In contrast, the short chain saturated phosphatidic acids, dilauroyl- and dimyristoylphosphatidic acids, undergo a condensation in the pH range 2 to 7. This is so in spite of the fact that the phosphoric acid group dissociates and the phosphatidic acid molecule attains one negative charge over this pH range. This finding is interpreted to indicate that the electrostatic repulsion between negatively charged phosphatidic acid molecules is compensated for or even outweighed by other intermolecular forces. Hydrogen bonding at the lipid/water interface is supposed to play a major role. All phosphatidates studied exhibit a significant expansion in the pH range 7 to 12. The second apparent pK of the primary phosphate group of phosphatidic acids is 8.6 and the expansion observed in this pH range is therefore due to electrostatic repulsion. At neutral pH the ether analogues of saturated phosphatidic acids have monolayer properties similar to those of the ester compounds. Considering the total pH range of 2 to 12 studied the force-area curves of the ether analogues are more condensed compared to the ester compounds. Synthetic phosphatidates and their ether analogues give reversible sharp crystal(gel)-to-liquid crystal transitions while the naturally occurring egg phosphatidate gives a broad, asymmetric one. The transition temperature Tm of saturated phosphatidates increases with increasing hydrocarbon chain length and at a given chain length Tm decreases markedly with unsaturation. The Tm values of the ether analogues are about 10 degrees C higher and the delta H values are 10-15% lower than those of the corresponding esters.
Calorimetry, Differential Scanning↗
Peripheral nerve P2 basic protein and the Guillain-Barré syndrome. In vitro demonstration of P2-specific antibody-secreting cells.
An immune response to the peripheral nerve basic protein P2 may be operative in the pathogenesis of the Guillain-Barré syndrome (GBS). A method is described for the purification of P2 of human origin. Purified P2 was used to investigate whether lymphocytes derived from peripheral blood of GBS patients are capable of producing P2-specific antibodies after stimulation with the antigen in vitro. Peripheral blood lymphocytes (PBL) from 5 GBS patients, from 3 patients with chronic idiopathic polyradiculoneuropathy (CIP) and from 3 normal controls were cultured in vitro in the presence of P2. PBL from the 5 GBS patients were shown to generate an antigen (P2)-specific antibody response. Contrariwise, PBL from the 3 CIP patients as well as from the 3 normal controls did not show this specific response.
Antibody Specificity↗
The full length of a mitochondrial presequence is required for efficient monolayer insertion and interbilayer contact formation.
The peptide specificity of both presequence-monolayer interactions and the ability of presequences to induce interbilayer contacts between large unilamellar vesicles was investigated. A range of different synthetic peptides that are documented for their mitochondrial protein import abilities were used for this purpose. Both monolayer insertion and vesicle aggregation were found to be strongly dependent on the primary structure of the studied presequence peptides. The combination of monolayer data and results of vesicle aggregation experiments leads to the overall suggestion that monolayer insertion and interbilayer contact formation are mechanistically related. For maximal effects the full length of a presequence peptide is required. The cardiolipin specificity of presequence-induced interbilayer contact formation previously reported was found to be a more general property among presequence peptides. The peptide's ability to induce vesicle-vesicle contacts seems to parallel the efficiency of its import ability into mitochondria. These results lead to an extended hypothesis on the role of presequence-induced contact site formation during the mitochondrial protein import process.
Adrenodoxin↗
The specificity of glycolipid-preferredoxin interaction: requirements for membrane binding.
Preferredoxin (prefd) is a precursor protein that is imported into chloroplasts. Monolayer experiments have shown that prefd has a high affinity for monogalactosyldiglyceride (MGaIDG) isolated from chloroplasts, which contains polyunsaturated fatty acid constituents and is therefore in a liquid-expanded state, but has been found to interact also with MGaIDG with long-chain saturated fatty acids, which exist in a gel state. For an optimal interaction, the fatty acid chain length and the extent of unsaturation are also important parameters, whereas the conformation of the sugar moiety, the sugar-glycerol or glycerol-hydrocarbon chain linkages are of little influence on the pressure changes measured in monomolecular layers. Conversely, steric hindrance of a methyl group at position 3 of the sugar largely inhibits the interaction. Quantification of the interaction with radiolabelled prefd shows that only a small part of the molecule is able to penetrate MGaIDG in the gel state, whereas a nearly four-times larger part is able to penetrate MGaIDG isolated from chloroplasts. It is likely that interactions of the transit sequence of prefd with the glycolytic head group MGaIDG are involved in targeting and binding to the chloroplast membrane.
Cell Membrane↗