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Biomedical subjects

R A Demel

Publications and source records attributed to R A Demel.

At least 91 records · Page 5Linked to original sources
PubMed1984

Effect of monolayer lipid structure and composition on the lipoprotein lipase-catalyzed hydrolysis of triacylglycerol.

The effect of lipid composition and structure on the lipoprotein lipase-catalyzed hydrolysis of triacylglycerols was determined in a monolayer system consisting of purified bovine milk lipoprotein lipase and fatty acid-free albumin. In a monolayer of dioleoylphosphatidylcholine containing 1-6 mol% of either tri[14C]oleoylglycerol or tri[14C] palmitoylglycerol , lipoprotein lipase catalyzed the hydrolysis of the unsaturated triacylglycerol at a higher rate than the saturated lipid and in either the presence or absence of apolipoprotein C-II, the activator protein for the enzyme. For example, with 3 mol% triacylglycerol and in the presence of apolipoprotein C-II, the rate of the lipoprotein lipase-catalyzed hydrolysis of tri[14C]oleoylglycerol was 27 mumol oleic acid produced/h per mg enzyme vs. 12 mumol for tri[14C] palmitoylglycerol . The effect of phospholipid fatty acyl chain length and unsaturation/saturation, polar head group and surface density on the lipoprotein lipase-catalyzed hydrolysis of tri[14C]oleoylglycerol was determined. The rate of enzyme hydrolysis of triacylglycerol was similar whether the phospholipid was a diester or diether lipid or the polar head group was ethanolamine or choline. In general, phospholipids with shorter and unsaturated fatty acyl chains gave higher rates of lipoprotein lipase hydrolysis of triacylglycerol than the corresponding longer and saturated lipids. However, with all phospholipids tested, the rate of enzyme hydrolysis decreased with increasing surface density. Lipoprotein lipase showed no activity toward triacylglycerol in a monolayer of sphingomyelin; addition of dioleoylphosphatidylcholine to the monolayer enhanced the rate of enzyme catalysis. Cholesterol (50 mol%) in a dipalmitoylphosphatidylcholine monolayer increased the rate of the lipoprotein lipase-catalyzed hydrolysis of tri[14C]oleoylglycerol, whereas cholesterol decreased the rate in a dioleoylphosphatidylcholine monolayer. The effect of phospholipid structure and surface density on lipoprotein lipase activity could not be accounted for by the amount of apolipoprotein C-II which was present at the interface. Based on these findings and other reports in the literature, we suggest that the catalytic activity of lipoprotein lipase toward tri[14C] oleylglycerol in various monolayers is dependent on the conformation or appropriate physical state of the triacylglycerol substrate at the lipid interface.

Animals↗
PubMed1984

The effect of the sterol oxygen function on the interaction with phospholipids.

The effect of cholesteryl ethers (namely cholesteryl methyl ether, cholesteryl ethyl ether, cholesteryl n-propyl ether, cholesteryl isopropyl ether, cholesteryl butyl ether, cholesteryl methoxymethyl ether, cholesteryl (2'-hydroxy)-3-ethyl ether) and cholesteryl ester (namely cholesteryl acetate) is tested on the interaction with phosphatidylcholines in liquid-crystalline and crystalline state. The interfacial properties of sterols are tested at the air-water interface. The cholesteryl ethers show a reduced interfacial stability with increasing hydrophobicity of the ether-linked moiety. The interaction between the sterol derivatives and phospholipids in mixed monolayers is indicated by measuring the deviation from the simple addivity rule (condensing effect). An interaction is found only for cholesteryl (2'-hydroxy)-3-ethyl ether, cholesteryl methyl ether and cholesteryl ethyl ether. These sterols also reduce the glucose permeability of liposomal membranes in this order. In this respect cholesteryl (2'-hydroxy)-3-ethyl ether is as effective as cholesterol. Cholesteryl methyl ether and cholesteryl ethyl ether show 62 and 33 percent of the effect observed with cholesterol. The effect of the sterol derivatives on the gel-to-liquid-crystalline phase transition of dipalmitoylphosphatidylcholine is measured by differential scanning calorimetry. Cholesteryl methyl ether, cholesteryl ethyl ether, and cholesteryl (2'-hydroxy)-3-ethyl ether reduce the energy content of the phase transition nearly as effective as cholesterol, cholesteryl n-propyl ether has only a small effect. Although cholesteryl acetate, and cholesteryl methoxymethyl ether have no condensing or permeability-reducing effect, they have a considerable effect on the gel-to-liquid-crystalline phase transition. Cholesteryl isopropyl ether and cholesteryl butyl ether have no effect. It is concluded that a free 3 beta-hydroxy group is not a prerequisite to observe a sterol-like effect in membranes. However, the interfacial stability and the orientation of the sterol and oxygen moiety at the sterol 3-position are important.

Calorimetry, Differential Scanning↗
PubMed1984

Sterol-phospholipid interactions in model membranes. Effect of polar group substitutions in the cholesterol side-chain at C20 and C22.

The interactions of phospholipids with four different cholesterol derivatives substituted with one OH or one keto group at position C20 or C22 of the side-chain were studied. The derivatives were the 22,R-hydroxy; 22,S-hydroxy; 22-keto- and 20,S-hydroxycholesterol. Two aspects of the interactions were investigated: (1) the effect of the cholesterol derivatives on the gel leads to liquid crystalline phase transition of dipalmitoylphosphatidylcholine (DPPC) and of dielaidoylphosphatidylethanolamine (DEPE) monitored by differential scanning calorimetry and (2) The effect on the lamellar leads to hexagonal HII phase transition of DEPE monitored by DSC and by 31P-NMR to determine structural changes. The gel leads to liquid crystalline phase transition was affected by the cholesterol derivatives to a much larger extent in the case of DPPC than of DEPE. In both cases, there was a differential effect of the four derivatives, the 22,R-hydroxycholesterol being the less effective. In DPPC-sterol 1:1 systems, 22,R-hydroxycholesterol does not suppress the melting transition, the delta H values becomes 7.1 kcal X mol-1 as compared to 8.2 kcal X mol-1 for the pure lipid. 22,S-OH cholesterol has a much stronger effect (delta H = 3.1 kcal X mol-1) and 22-ketocholesterol suppresses the transition completely. In DEPE mixtures of all these compounds, the melting transition of the phospholipid is still observable. The transition temperature was shifted to lower values (-13.5 degrees C in the presence of 20,S-OH cholesterol). The delta H of the transition was lowered by these compounds except in DEPE-22,R-OH cholesterol mixtures and the cooperativity of the transition (reflected by the width at half peak height) was reduced. The lamellar leads to hexagonal HII phase transition was also affected by the presence of these cholesterol derivatives. The transition temperature value was depressed with all these compounds. 20,S-OH cholesterol was the most effective followed by 22,R-OH cholesterol. The delta H of the transition was not strongly affected. The molecular interfacial properties of these derivatives were studied by the monomolecular film technique. It is most likely that 22,R-OH cholesterol due to the hydroxyl groups at the 3 beta- and 22,R-positions orients with the sterol nucleus lying flat at the air/water interface, since the compression isotherm of either the pure sterol or the DOPC-sterol mixture (molar ratio, 1:1) monomolecular film exhibits a transition at approx. 103 A2.(ABSTRACT TRUNCATED AT 400 WORDS)

Air↗
PubMed1984

Interactions of hemin, antimalarial drugs and hemin-antimalarial complexes with phospholipid monolayers.

Hemin, antimalarial drugs and complexes formed between them, have demonstrable effects on biological membranes. Using the phospholipid monolayer model, we show that hemin intercalates into the membrane and increases its surface pressure, depending on the lipid composition and the initial surface pressure: negative surface charges and particularly looser compaction of the phospholipids reduce the effect of hemin. With increasing surface pressure hemin tends to intercalate as a monomer, and the half-saturation concentration of its effect increases exponentially. The antimalarial monovalent drugs quinine and mefloquine, but not chloroquine, also penetrate into the membrane and expand it. All three drugs markedly increase the effect of hemin, but chloroquine reduces the effect in monolayers composed of unsaturated phospholipids. The drugs' effect is mostly due to an increase in the maximal surface pressure and suggests a complexation of hemin and drug within the membrane phase. Preformed hemin-drug complexes decrease the half-saturation concentration of the effect and suggest that the complexes adsorb to the membrane, releasing the hemin through an apolar continuum into the phospholipid phase. The implications of the results to the membrane toxicity mechanism proposed for the molecular mode of action of antimalarial drugs are discussed.

Animals↗
PubMed1984

Morphological and biochemical changes in myelin subfractions of developing rats fed microbial lipids.

Morphological, biochemical, and physicochemical studies of myelin subfractions were undertaken on the progeny of Sprague-Dawley rats fed diets containing lipids either extracted from yeasts grown on n-alkanes or from margarine. Myelin subfractions obtained from pooled brain homogenates of littermates by sucrose density gradient centrifugation at 7, 14, and 21 days postnatally were subjected to electron microscopy, sodium dodecylsulfate polyacrylamide gel electrophoresis and assayed for 2', 3' cyclic nucleotide 3'-phosphohydrolase activity (CNPase; EC 3.1.4.37). Additionally, surface pressure measurements were made of lipid monolayers derived from myelin subfractions, which were subsequently injected with myelin basic proteins. The myelin subfractions of test animals, when compared with those of controls, show an earlier increase in the specific activity of CNPase, the earlier appearance of low-molecular-weight proteins, and an increase in the affinity of basic proteins for lipids derived from the myelin light fraction. This biochemistry suggests the presence of a more mature myelin between 7 and 14 days in the experimental group. The morphological studies, however, do not seem to concur with the biochemical data. The observed changes are discussed in relation to the influence of dietary lipids on myelinogenesis.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1983

The effect of ferriprotoporphyrin IX and chloroquine on phospholipid monolayers and the possible implications to antimalarial activity.

Ferriprotoporphyrin IX intercalates into phospholipid membranes, as evidenced from its effect on the surface pressure of monolayers composed of different phospholipids. Ferriprotoporphyrin intercalation is enhanced by membrane hydrophobicity and decreased by negative surface potential. Chloroquine enhances the effect of ferriprotoporphyrin in relatively hydrophobic membranes but reduces it in monolayers composed of highly unsaturated phospholipids. These results are consistent with the differential effect of chloroquine on ferriprotoporphyrin-induced lysis of erythrocytes and of malarial parasites, thus supporting the membrane-lesion hypothesis of antimalarial action.

Chloroquine↗
PubMed1982

Lipoprotein lipase-catalyzed hydrolysis of tri[14C]oleoylglycerol in a phospholipid interface. A monolayer study.

The lipoprotein lipase-catalyzed hydrolysis of triacylglycerol was determined in a lipid monolayer containing egg phosphatidylcholine and tri[14C]oleoylglycerol. In the presence of purified bovine milk lipoprotein lipase and fatty acid-free albumin, the rate of hydrolysis of tri[14C]oleoylglycerol, as determined by the decrease in surface activity, was dependent upon enzyme concentration and was enhanced by the addition of apolipoprotein C-II, the activator protein for the enzyme. Increasing the triacylglycerol content of the phospholipid monolayer from 1 to 6 mol% (relative to phospholipid) enhanced the rate of catalysis in the presence and absence of apolipoprotein C-II. However, at low substrate concentrations (less than 4 mol% tri[14C]oleoylglycerol), the activation factor for apolipoprotein C-II was greater than at high (4-6 mol%) triacylglycerol concentrations. The addition of sphingomyelin to the phosphatidylcholine monolayer decreased lipoprotein lipase activity. Based on these monolayer studies, we conclude that lipoprotein lipase catalyzes the hydrolysis of triacylglycerol at a phospholipid interface and that the rate of catalysis is dependent on the lipid composition of the monolayer.

Animals↗
PubMed1982

Interaction of a human plasma lipid transfer protein complex with lipid monolayers.

The interaction of a purified human plasma lipid transfer complex with cholesteryl ester, triacylglycerol and phosphatidylcholine in binary and ternary lipid monolayers was investigated. The lipid transfer complex, designated LTC, catalyzes the removal of cholesteryl oleate and triacylglycerol from phosphatidylcholine monolayers. Preincubation of LTC with p-chloromercuriphenyl sulfonate inhibits LTC-catalyzed removal of triacylglycerol; cholesteryl ester removal is not affected. The rate of LTC-facilitated removal of cholesteryl oleate from a phosphatidylcholine monolayer depends on the amount of LTC added to the subphase up to 100 micrograms protein. In addition, the rate of the LTC-catalyzed transfer of cholesteryl oleate to the subphase increases linearly as the amount of cholesteryl oleate in the monolayer increases to 6 mol%. LTC also removes cholesterol from phosphatidylcholine-cholesterol monolayers, albeit at a rate which is 15% of that for removal of cholesteryl oleate. The ability of LTC to facilitate triacylglycerol and cholesteryl ester removal depends on the composition of the monolayer. Phosphatidylcholine supports cholesteryl ester transfer whereas sphingomyelin-cholesteryl ester monolayers are almost refractory to LTC. In contrast, LTC removes triacylglycerol from either a phosphatidylcholine or a sphingomyelin monolayer. The results suggest the existence of at least two lipid transfer proteins, one of which catalyzes the removal of cholesteryl ester and the other triacylglycerol. The role of these proteins as they relate to lipoprotein metabolism is discussed.

Carrier Proteins↗
PubMed1982

Transfer properties of the bovine brain phospholipid transfer protein. Effect of charged phospholipids and of phosphatidylcholine fatty acid composition.

The monolayer technique has been used to study the transfer of [14C]phosphatidylinositol from the monolayer to phosphatidylcholine vesicles. An equivalent transfer rate was found for egg phosphatidylcholine, dioleoylphosphatidylcholine, dielaidoylphosphatidylcholine and dipalmitoylphosphatidylcholine. A reduced transfer rate was found for a shorter-chain derivative, dimyristoylphosphatidylcholine, and for species with two polyunsaturated fatty acid chains such as dilinoleoylphosphatidylcholine, diheptadecadienoylphosphatidylcholine, dilinolenoylphosphatidylcholine and diether and dialkyl derivatives. No activity was found for 1,3-dipalmitoylphosphatidylcholine. The presence of up to 5 mol% phosphatidylinositol in egg phosphatidylcholine vesicles had no effect on the transfer rate. Introduction of more than 5 mol% phosphatidylinositol or phosphatidic acid into the phosphatidylcholine vesicles gradually decreased the rate of phosphatidylinositol transfer from the monolayer. 20 mol% acidic phospholipid was nearly completely inhibitory. Transfer experiments between separate monolayers of phosphatidylcholine and phosphatidylinositol showed that the protein-bound phosphatidylcholine is readily exchanged for phosphatidylinositol, but the protein-bound phosphatidylinositol exchange for phosphatidylcholine occurs at a 20-times lower rate. The release of phosphatidylinositol is dependent on the lipid composition and the concentration of charged lipid in the acceptor membrane, but also on the ratio between donor and acceptor membranes. The main transfer protein from bovine brain which transfers phosphatidylinositol and phosphatidylcholine transfers also phosphatidylglycerol, but not phosphatidylserine or phosphatidic acid. The absence of significant changes in the surface pressure indicate that the phosphatidylinositol and phosphatidylcholine transfer is not accompanied by net mass transfer.

Animals↗
PubMed1982

Transfer properties of the bovine brain phospholipid transfer protein. Specificity towards phosphatidylcholine analogs and the inhibitory effect of sphingomyelin.

A coupled transport of phosphatidylinositol from the monolayer to phosphatidylcholine vesicles, and a phosphatidylcholine transport in the reverse direction in the presence of bovine brain transfer protein is demonstrated. No significant amounts of protein accumulate at the interface during the transfer reaction. The transfer protein from bovine brain shows a lower specificity for phosphatidylcholine than does the transfer protein from bovine liver. Relative to egg phosphatidylcholine a low transfer rate is found for derivatives with a chain length of 14 carbon atoms and a distance between phosphorus and nitrogen of 6 carbon atoms. The gel state of phosphatidylcholine does not reduce the transfer reaction as catalyzed by the bovine brain protein. The transfer of phosphatidylinositol is inhibited by sphingomyelin. The presence of 200 mM K+ or 1mM Ca2+ does not affect the transfer activity of the bovine brain protein. Divalent ions at concentrations higher than 5 mM cause a fusion of vesicles with monolayers. The pH optimum of the phosphatidylinositol transfer reaction is 8.

Animals↗
PubMed1981

The effect of 5-(n-alk(en)yl) resorcinols from rye on membrane structure.

The increased membrane permeability for K+, glycerol and erythritol, and membrane lysis induced by alkyl and alkenyl resorcinols, respectively, might be due to the interaction with membrane proteins and the formation of reversed micelles. The 5-(n-alk(en)yl) resorcinols show a very high stability at the air/water interface. The molecular area is 0.28 and 0.37 nm2 (at 30 mN/m) for alkyl and alkenyl resorcinols from rye, respectively. Differential scanning calorimetry experiments show a miscibility of alk(en)yl resorcinols with phosphatidylcholines. Only for alkenyl resorcinols is a small reduction found in the free energy of dipalmitoyl phosphatidylcholine. Electron microscopy studies show protein patching in erythrocyte membranes after the addition of resorcinols. The resorcinol-induced K+ release is not influenced by the presence of proteolytic enzymes, but strongly reduced by bovine serum albumin and glycophorin. 31P-NMR measurements show the occurrence of an isotropic and hexagonal signal in egg phosphatidylcholine in the presence of about 30 mol% alk(en)yl resorcinol.

Animals↗
PubMed1980

Permeability changes of erythrocytes and liposomes by 5-(n-alk(en)yl) resorcinols from rye.

5-(n-Alk(en)yl) resorcinols can induce potassium release from liposomes and erythrocytes. The results suggest that 5-(n-pentyl)resorcinol can induce a specific permeability to protons as well as to potassium and other small molecules. The highest permeability changes were found in the presence of 5-(n-pentadecyl)resorcinol and alkenyl resorcinols. Orcin and resorcin were without effect. The size of permeant as investigated by turbidity measurements indicated that Ca2+ and Mg2+ cannot pass through the alkyl resorcinol-modified membrane but can pass through the alkenyl resorcinol-modified membrane. It was observed that alkenyl resorcinol at a concentration of 15 microM induced not only potassium release but also lysis of erythrocytes.

Animals↗
PubMed1980

Spectrin-phospholipid interaction. A monolayer study.

(1) The interaction of synthetic and natural phospholipids with spectrin, purified from human erythrocyte membranes, was studied using the monolayer technique at constant surface pressure. Spectrin penetration into the lipid monolayer was recorded as the rate of surface area increase on a two-compartment trough. (2) High spectrin penetration rates were observed with negatively charged phospholipids while zwitterionic or neutral lipids showed only poor spectrin affinity. This penetration rate was strongly affected by the subphase pH. At pH 5.5, maximal pentration rates wre obsreved for phosphatidylglycerol and phosphatidylserine but not for phosphatidylcholine. (3) In comparing the penetration rates for phospholipids with a natural fatty acid composition and the dimyristoyl species of phosphatidic acid, phosphatidylglycerol, phosphatidylserine and phosphatidylcholine, the lipid fatty acid composition proved to be an important parameter. The differences are collelated with the area per lipid molecule. (4) Other parameters affecting the area per lipid molecule such as surface pressure, pH and salt concentration also strongly influenced spectrin penetration rates for negatively charged phospholipids. Spectrin penetration into phosphatidylcholine monolayers is only slightly affected by variation of these conditions. (5) The effect of Ca2+ on spectrin-lipid interactions was studied for several phosphatidylglycerol and phosphatidylserine species. Both lipids condensed upon the addition of Ca2+, but only in the case of the phosphatidyleserine was this accompanied by extrusion of the spectrin from the interface, which is in agreement with earlier calorimetric experiments with bilayer systems of analogous composition (Mombers, C., Verkleij, A.J., de Gier, J. and van Deenen, L.L.M. (1979) Biochim. Biophys. Acta 551, 271-281). For this phenomenon a model is presented.

Calcium↗
PubMed1980

The action of pimaricin, etruscomycin and amphotericin B on liposomes with varying sterol content.

1. The effect of pimaricin, etruscomycin and amphotericin B on the K+ release from liposomes is strongly dependent on their sterol concentration. Pimaricin and etruscomycin induce K+ release from egg lecithin liposomes with cholesterol contents of more than 25 and 10 mol%, respectively, at polyene concentrations of 100 and 10 microgram/ml, respectively. Amphotericin B shows a maximal effect at a cholesterol content of 20 mol% at a concentration of 0.4 microgram/ml. 2. For liposomes containing ergosterol the sensitivity is shifted to a lower sterol content. All three polyenes show activity at 10 mol% ergosterol. The sensitivity for amphothericin B is increased approx. 15 times by the incorporation of ergosterol compared to cholesterol. The increase in sensitivity is much less for pimaricin and etruscomycin. The K+ release is maximal at an ergosterol concentration of 30 mol%. 3. Pimaricin, etruscomycin and amphotericin B can induce K+ release from erythrocytes without the release of haemoglobin at concentrations of 20, 2 and 1 microgram/ml, respectively. For these polyenes a selective permeability change is also demonstrated for liposomes since K+ is released but no [14C]dextran. Filipin shows a nonselective release of solutes from erythrocytes and liposomes. 4. At cholesterol concentrations higher than 20 mol% and ergosterol concentrations higher than 10 mol%, etruscomycin, pimaricin and amphotericin B show little dependence of the bilayer thickness and are able to release K+ from didocosenoyl phosphatidylcholine liposomes after addition of the polyene to one side of the membrane. A possible mechanism is discussed.

Amphotericin B↗
PubMed1979

Interaction of plasma apolipoproteins with lipid monolayers.

The monolayer technique has been used to study the interaction of lipids with plasma apolipoproteins. Apolipoprotein C-II and C-III from human very low density lipoproteins, apolipoprotein A-I from human high density lipoproteins and arginine-rich protein from swine very low density lipoproteins were studied. The injection of each apoprotein underneath a monolayer of egg phosphatidy[14C]choline at 20 mN/m caused an increase in surface pressure to approximately 30 mN/m. With apolipoprotein C-II and apolipoprotein C-III there was a decrease in surface radioactivity indicating that the apoproteins were removing phospholipid from the interface; the removal of phospholipid was specific for apolipoprotein C-II and apolipoprotein C-III. Although there was a removal of phospholipid from the monolayer, the surface pressure remained constant and was due to the accumulation of apoprotein at the interface. The rate of surface radioactivity decrease was a function of protein concentration, required lipid in a fluid state and, of the lipids tested, was specific for phosphatidylcholine. Cholesterol and phosphatidylinositol were not removed from the interface. The addition of 33 mol% cholesterol to the phosphatidylcholine monolayer did not affect the removal of phospholipids by apolipoprotein C-III. The addition of phospholipid liposomes to the subphase greatly facilitated the apolipoprotein C-II-mediated removal of phospholipid from the interface. Although apolipoprotein A-I and arginine-rich protein gave surface pressure increases, phospholipid was only slightly removed fromthe interface by the addition of liposomes. Based on these findings, we conclude that the apolipoproteins C interact specifically with phosphatidylcholine at the interface. This interaction is important as it relates to the transfer of the apolipoproteins C and phospholipids from very low density lipoproteins to other plasma lipoproteins. The addition of human plasma high density lipoproteins or very low density lipoproteins to the subphase increased the apolipoprotein C-mediated removal of phosphatidyl[14C]choline from the interface 3--4 fold. Low density lipoproteins did not affect the rate of decrease. During lipolysis of very low density lipoproteins to the subphase increased the apolipoprotein C-mediated removal of with the lipid monolayer. Lipolysis experiments were performed in a monolayer trough containing a surface film of egg phosphatidyl[14C]choline and a subphase of very low density lipoproteins and bovine serum albumin. Lipolysis was initiated by the addition of purified milk lipoprotein lipase to the subphase. As a result of lipolysis, there was a decrease in surface radioactivity of phosphatidylcholine. The pre-addition of high density lipoproteins decreased the rate of decrease in surface radioactivity...

Animals↗
PubMed1978

Interaction of the acetylcholine (nicotinic) receptor protein from Torpedo marmorata electric organ with monolayers of pure lipids.

Membrane fragments rich in cholinergic (nicotinic) receptor protein were purified from the electric organ of Torpedo marmorata. Their lipid composition is essentially characterized by the prominence of cholesterol, phosphatidylethanolamine and phosphatidylcholine, long-chain fatty acyl constituents, and the absence of sphingomyelin. Solubilised receptor was purified from these fragments and the concentration of sodium cholate lowered by dialysis to 0.01% (w/v). When this preparation was injected under a lipid monolayer, an increase of surface pressure developed, which was not observed with the detergent alone nor in the absence of lipid film. When covalently radiolabelled receptor preparations were injected at a constant surface pressure the radioactivity recovered with the film was proportional to the increase in area. It is concluded that the pressure or area increases are due to the penetration of the cholinergic receptor protein into the lipid film. Incorporation experiments into films formed from various pure lipids showed that the protein interacts more readily with cholesterol than with ergosterol, phosphatidylcholine, or other phospholipids. Its affinity is also higher for long-chain phosphatidylcholines than for short-chain ones. The degree of unsaturation and fluidity of the 3-sn-phosphatidylcholine (lecithin) films are of secondary importance. Parallel experiments with covalently and non-covalently labelled receptor preparations showed that part of the protein recovered with the film lost its alpha-toxin binding ability during the penetration. Similar data were obtained with the receptor purified from Electrophorus electricus electric organ.

Animals↗
PubMed1977

Specific interaction of concanavalin A with glycolipid monolayers.

The effect of 131I-labelled concanavalin A on the surface pressure and surface radioactivity of monolayers formed from phospholipids and from natural and synthetic glycolipids has been studied. The lectin binds to and penetrates dipalmitoyl phosphatidylcholine monolayers at a surface pressure of 15 dynes/cm and this interaction is inhibited by the presence of alpha-methyl mannose in the subphase. At surface pressures of 25 dynes/cm or higher, concanavalin A will interact with monoglucosyl diglyceride or diglucosyl diglyceride from Acholeplasma laidlawii and with synthetic glycolipids containing 2 or 3 alpha 1 leads to 4-linked D-glucose residues in the headgroup, but not with phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, or with the ganglioside II3NeuAc-GgOse4-Cer. The binding to the glycolipid sugar group and penetration of the hydrocarbon region seem to occur simultaneously, as the time courses for the development of surface pressure and surface radioactivity coincide.

Cell Membrane↗