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At least 19 recordsLinked to original sources
PubMed1976

Activity of cholinephosphotransferase, lysolecithin: lysolecithin acyltransferase and lysolecithin acyltransferase in the developing mouse lung.

1. The present study presents the activity profiles of cholinephosphotransferase, lysolecithin:lysolecithin acyltransferase and lysolecithin acyltransferase at different stages of development of the mouse lung. 2. The specific activity of cholinephosphotransferase, a key enzyme in the de novo synthesis of phosphatidylcholine, increases during the later stages of fetal development until it reaches a maximal value at a gestational age of 17 days, i.e. 2 days before term. Thereafter, the activity of the enzyme declines again until around term. 2. The specific activity of lysolecithin:lysolecithin acyltransferase which catalyzes the transesterification between two molecules of 1-acyl-sn-glycero-3-phosphocholine, appears to be much lower than that of cholinephosphotransferase at gestational ages below 18 days. However, around day 18, the specific activity of lysolecithin:lysolecithin acyltransferase increases dramatically until it almost equals the maximal activity of cholinephosphotransferase measured on day 17. 4. The specific activity of lysolecithin acyltransferase, which catalyzes the direct acylation of 1-acyl-sn-glycero-3-phosphocholine, does not change significantly during the prenatal development and is lower than that of either lysolecithin:lysolecithin acyltransferase or cholinephosphotransferase at all stages of development. 5. These results are discussed in view of the possible role of these enzymes in the biosynthesis of pulmonary 1,2-dipalmitoyl-sn-glycero-3-phosphocholine.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1979

Lysolecithin acyltransferase and lysolecithin: lysolecithin acyltransferase in adult rat lung alveolar type II epithelial cells.

1. The specific activity of lysolecithin acyltransferase (EC 2.3.1.23) in sonicated adult rat lung alveolar type II epithelial cells, measured either alone or in combination with acyl-CoA synthetase (EC 6.2.1.3), was found to be an order of magnitude greater than that of lysolecithin:lysolecithin acyltransferase. 2. Lysolecithin acyltransferase in type II cells was found to prefer palmitoyl-CoA over oleoyl-CoA as substrate. The combination of lysolecithin acyltransferase and acyl-CoA synthetase was found to prefer palmitate over oleate for incorporation into phosphatidylcholine. 3. Compared to whole lung homogenate, sonicated adult rat type II cells are highly enriched in lysolecithin acyltransferase but not in lysolecithin:lysolecithin acyltransferase. 4. These observations indicate that in normal adult rat type II cells the deacylation-reacylation cycle is more important for the formation of dipalmitoyl phosphatidylcholine than the deacylation-transacylation process.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1990

Effect of albumin on acyl-CoA: lysolecithin acyltransferase, lysolecithin: lysolecithin acyltransferase and acyl-CoA hydrolase from rabbit lung.

Acyl-CoA: lysolecithin and lysolecithin: lysolecithin acyltransferases, as well as acyl-CoA hydrolase are important enzymes in lung lipid metabolism. They use amphiphylic lipids as substrates and differ in subcellular localization. In this sense, lipid-protein interactions can be an essential factor in their activity. We have studied the effect of albumin, as lipid-binding protein model, in the activities of these enzymes. Acyl-CoA hydrolase was inhibited in the presence of albumin, whereas acyl-CoA: lysolecithin acyltransferase showed a complex effect of activation depending on both albumin concentration and palmitoyl-CoA/lysolecithin molar ratio. Lysolecithin: lysolecithin acyltransferase was affected differentially on its two activities. Hydrolysis remained unaffected and transacylation was inhibited by albumin. These results are consequence of the interaction of albumin with both lipidic substrates that changes their critical micellar concentration.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1975

Lysolecithin and cholesterol interact stoichiometrically forming bimolecular lamellar structures in the presence of excess water, of lysolecithin or cholesterol.

The structural interaction of egg lysolecithin, derived from egg lecithin, and cholesterol in aqueous solution has been investigated using X-ray diffraction. When mixed in any proportions, either suspended in excess buffer or up to 85% lipid by dry weight, a separate lamellar phase containing equimolar proportions of lysolecithin and cholesterol forms, separate from excess water, or lysolecithin or cholesterol. The cholesterol disorders the crystalline chains of the lysolecithin. The equimolar phase is stable up to 50 degrees C unlike lysolecithin alone, which forms micelles, Thes results show that lysolecithin and cholesterol combine stoichiometrically in a stable complex. We propose as a structural model, that cholesterol fills the space of the missing fatty acyl chain making the lysolecithin more cylindrical rather than wedge shaped. This interaction could reduce both the lytic action of lysolecithin on membranes and its induction of cell fusion. It suggest another role of cholesterol in cell membranes: namely, to act as a stabilizer of bilayer structure by being a mobile component that can fill free volume in the hydrocarbon interior. Lysolecithin-cholesterol interaction may also be important in the early events of atherosclerosis where lysolecithin levels in vessel walls increase fivefold.

Binding Sites↗
PubMed1976

Quantitative studies on lysolecithin mediated hemolysis. Benzylated lysolecithin as a probe to study effects of temperature and red cell species on the hemolytic reaction.

The slow reacting hemolytic lysolecithin analog 1-octadecyl-2-benzyl-glycero-3-phosphorylcholine has been employed for a detailed study of the process of lysolecithin induced hemolysis. Using a radiolabelled analog we found that the different sensitivities of red cells from different species (chicken, man, cattle) are not paralleled by the binding affinities of lysolecithin. Moreover, lysophosphatide binding to the cells is reduced at low temperatures while the hemolytic activity increases. In contrast to continuous changes of lytic activity and binding between 0 and 37 degrees C, the velocity of the hemolytic reaction with human erythrocytes is extraordinarily fast at 10 degrees C. Experiments in sucrose containing buffer indicated principally different lysis mechanisms below and above 15 degrees C. We have further shown that cells loaded sublytically with the lysolecithin at 37 degrees C undergo spontaneous lysis upon cooling to 0 degrees C. The degree of lysis under these conditions, however, is diminished with increasing amounts of cell-bound lysolipid. Determinations of membrane microviscosities by means of fluorescence polarization revealed some qualitative relations between membrane fluidity and sensitivity to lysolecithin. The data are discussed on the basis of recent reports indicating that lysolecithin-distribution in mixed lipid phases may be heterogeneous depending on lipid composition and temperature.

Animals↗
PubMed1977

Quantitative studies on lysolecithin-mediated hemolysis. Use of ether-deoxy lysolecithin analogs with varying aliphatic chain-lengths.

The process of lysolecithin-mediated hemolysis has been investigated by use of various ether-deoxy lysolecithin analogs (1-alkyl-propanediol-3-phosphorylcholine) with alkyl residues of 10-22 carbon atoms. Hemolytic activities were defined either as molar amounts to be added for 50% lysis (L50) or as cell-bound amounts at 50% lysis (A50). It was found, that in contrast to L50, A50 values are independent of experimental conditions. Moreover, L50 values primarily reflect the binding affinities, while A50 values give more accurate information on the actual membrane-disturbing potential. The strongest hemolytic C16-lysolecithin analog required 2 - 10(7) or 5 - 10(7) molecules bound per cell for 50% lysis at 0 or 37degrees C, respectively, corresponding to about 10 or 25% of the total membrane phospholipids. Evidence is presented, indicating that (a) lysophosphatides bind to cells below their critical micelle concentration, (b) micelles themselves are not generally necessary for cell lysis. Red cells of different species (man and cattle) as well as at varying temperatures exhibit significantly different sensitivities in terms of L50 and A50 values. These differences, however, depend on the degree of hydrophobicity of the lysolecithins and disappear in the case of lysolipids having C10 or C12 aliphatic residues. The data are in agreement with our hypothesis that cellular sensitivity to lysolecithin lysis may be determined by the degree of segregation of lysolecithin-rich areas within the membrane lipid phase.

Animals↗
PubMed1980

Low density lipoprotein-activated lysolecithin acylation by human plasma lecithin-cholesterol acyltransferase. Identity of lysolecithin acyltransferase and lecithin-cholesterol acyltransferase.

There is in normal plasma an enzyme activity which converts labeled lysolecithin to lecithin by an energy-independent low density lipoprotein-activated pathway. Studies were undertaken to compare the identity of this enzyme with lecithin-cholesterol acyltransferase. During purification of the enzyme by ultracentrifugation and by chromatography on high density lipoprotein affinity column, DEAE-Sepharose column, and hydroxylapatite column, both the lysolecithin acyltransferase activity and the lecithin-cholesterol acyl transferase activity were found in the same fractions and were enriched to the same extent at each step. The final purified preparation which had 16,000- to 24,000-fold higher specific activities than starting plasma gave a single protein band on polyacrylamide gel electrophoresis and this single band contained both the activities. Also, the effects of pH, heat, and chemical inhibitors on the enzyme activities were similar. Plasma from patients with familial lecithin-cholesterol acyltransferase deficiency also lacked lysolecithin acyltransferase activity. These results indicate that a single enzyme carries out both lecithin-cholesterol acyltransferase and lysolecithin acyltransferase activities. The purified enzyme required apolipoprotein A-I for lecithin-cholesterol acyltransferase activity, but required low density lipoprotein for lysolecithin acyltransferase activity.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1984

Effect of lipids on activity and conformation of lysolecithin:lysolecithin acyltransferase from rabbit lung.

Lysolecithin:lysolecithin catalyzing two types of reaction, transacylation or hydrolysis, with the same substrate. Both activities have shown to be dependent on several environmental conditions and among them, the presence of lipids. The addition of several classes of lipids activated in all the cases the enzyme, decreasing the hydrolysis/transacylation molar ratio. This effect was higher for PC/PE/Chol mixture than for other lipids assayed. Circular dichroism spectra of the enzyme did not show any change with the addition of lipids, concluding that the effect of lipids was not due to any structural change in the protein. The hypothesis has been made of an influence of lipids on the physical state of the substrate as well as, possibly, on the enzyme-substrate interaction. The significance of these effects on the physiological role of lysolecithin-lysolecithin acyltransferase from soluble fraction of rabbit lung is discussed.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1975

Studies on lysophospholipases, V. The action of lysolecithin-hydrolyzing enzymes on lecithins and 1-acyl lysolecithins with varying fatty acid chain-length.

The activity of two purified lysolecithin-hydrolyzing enzymes on homologous series of synthetic lecithins containing two identical fatty acyl chains and of 1-acyl-lysolecithins has been measured as a function of substrate concentration. In general, enzymatic activity toward lecithins decreased with increasing chain length. Maximal hydrolysis rates for the lysolecithin series were measured with 1-dodecanoyllysolecithin. In this series increased affinities for substrates with increasing acyl-chain length was noticed. In the substrate concentration versus enzymatic velocity curves no breaks were observed at the critical micelle concentration of the various substrates. The initial site of attack during hydrolysis of short-chain lecithins was determined using 1-octanoyl-2pentanoyl-lecithin, 1-hexanoyl-2-hexyllecithin and 1 -hexyl-2-hexanoyllecithin. Both enzymes exhibited a pronounced preference for hydrolysis of the acyl ester bond at the 1-position. Especially the enzyme from beef pancreas seems to be suitable for the enzymatic preparation of 2-acyl lysolecithins from the corresponding short-chain lecithins.

Animals↗
PubMed1982

Incorporation kinetics of lysolecithin into lecithin vesicles. Kinetics of lysolecithin-induced vesicle fusion.

The incorporation kinetics of L-palmitoylphosphatidylcholine (lysolecithin) into dimyristoyl- and dipalmitoylphosphatidylcholine vesicles and the subsequent aggregation and fusion of the vesicles into larger aggregates were studied by using stopped-flow rapid-mixing techniques. The half-times for the lysolecithin incorporation vary between 50 and 500 ms. The incorporation rate has a maximum in the temperature range of the vesicle phase transition. This process is not diffusion controlled. The rate-limiting step is the incorporation of the lysolecithin monomer into the liquid bilayer. After this fast process, a slow reaction in the 10-50-min time range is observed. The large irreversible increase in turbidity indicates aggregation and fusion of the vesicles. The initial step is a second-order reaction with respect to the vesicle concentration, indicating aggregation or fusion of two vesicles. The aggregation rate passes through a maximum at the phase transition temperature.

Dimyristoylphosphatidylcholine↗
PubMed1984

Lysolecithin:lysolecithin acyltransferase from rabbit lung. A conformational study.

The enzyme lysolecithin:lysolecithin acyltransferase from rabbit lung has been found to have a relatively disordered conformation in solutions of high ionic strength. The protein exhibited an ordering of structure when salt was suppressed. This conformational change was concomitant with the loss of transacylase activity, the hydrolytic reaction remaining unchanged. Addition of NaCl caused a progressive disordering of structure with a parallel increase of transacylase activity. The acid denaturation of the protein, at low and high ionic strengths, showed that the ionization of groups with pK in the range 5.9-6.4 was essential for denaturation. The structure was stable at basic pH. The addition of lipids resulted in a non-specific stabilization of the disordered conformation, in the same manner as the addition of NaCl. From these results, it is suggested that there are two conformations for this protein which differ in their ability to bind lysolecithin molecules in the enzyme deacylation step of the reaction. This hypothesis agrees with previously published properties of the enzyme, concerning aggregation with other proteins and kinetic data. From the amino acid composition and conformational properties, the authors suggest that this enzyme could be a peripheral membrane protein.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1989

Essential histidine residues in lysolecithin:lysolecithin acetyltransferase from rabbit lung.

Both activities of rabbit lung lysolecithin:lysolecithin acyltransferase (EC 3.1.1.5), hydrolysis and transacylation, are inactivated by diethylpyrocarbonate. The reaction follows pseudo-first-order kinetics, and second-order rate constants of 1.17 mM-1min-1 for hydrolysis and 0.56 mM-1 min-1 for transacylation were obtained at pH 6.5 and 37 degrees C. The rate of inactivation is dependent on pH, showing the involvement of a group with a pK of 6.5. The difference spectra showed an increase in absorbance at 242 nm, indicating the modification of histidine residues. The activity lost by diethylpyrocarbonate modification can be partially recovered by hydroxylamine treatment. The statistical analysis of residual fractional activity versus the number of modified histidine residues leads to the conclusion that two histidine residues are essential for the hydrolytic activity, whereas transacylation activity depends on only one essential histidine. The substrate and substrate analogs protected the enzyme against inactivation by diethylpyrocarbonate, suggesting that the essential residues are located at or near the active site of the enzyme.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1990

Essential residues in lysolecithin:lysolecithin acyltransferase from rabbit lung: assessment by chemical modification.

The inhibition of lysolecithin:lysolecithin acyltransferase by several specific reagents was studied. Diisopropyl fluorophosphate (DFP) completely inhibited both activities at a concentration of 4 mM. Activity was not protected by substrate and the enzyme showed a change in circular dichroism spectrum upon treatment with inhibitor. Phenylmethanesulfonyl fluoride, another serine-specific reagent, did not inhibit either hydrolysis or transacylation. Therefore, we suggest that DFP does not modify an active serine in the catalytic site. p-Hydroxymercury benzoate and N-ethylmaleimide (NEM) abolished both activities of the enzyme. The presence of substrate partially protected against inactivation. Far-uv CD spectrum of NEM-modified enzyme revealed no changes in protein structure. The existence of two classes of essential cysteine residues was deduced from kinetics of NEM inactivation. Both classes differ in NEM reactivity and also in their participation in the catalytic mechanism. A tyrosine-specific reagent, tetranitromethane, also inhibited hydrolysis and transacylation, following first-order kinetics. The partial protection by substrate suggested the possible existence of essential tyrosines near the active site. At pH 5.0 N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline inactivated hydrolysis but not transacylation. However, both of them remained unchanged at pH 6.5. The substrate prevented the loss of hydrolytic ability. Therefore, a carboxyl residue participating just in the catalytic mechanism of hydrolysis is proposed.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1967

The chemical nature of the products obtained by the action of cabbage-leaf phospholipase D on lysolecithin: the structure of lysolecithin.

1. Lysolecithin, prepared by the action of snake-venom phospholipase A on ovolecithin, when incubated with Savoy-cabbage phospholipase D, in the presence of Ca(2+) ions, gave two degradation products (designated A and B) in the form of their calcium salts. 2. These calcium salts were separated quantitatively by solvent fractionation and converted into the corresponding sodium salts. 3. Substance B proved to be a lysophosphatidic acid of conventional structure (1-monoacyl-l-3-glycerophosphoric acid). When the phosphate group was removed by means of prostatic acid phosphomonoesterase, a 1-monoglyceride was formed quantitatively. Alkaline hydrolysis gave the theoretical yield of l-3-glycerophosphate. 4. Substance A, on the other hand, had all the properties expected for a cyclic phosphate of a 1-monoglyceride. It was unaffected by phosphomonoesterase. On alkaline hydrolysis, the acyl group was removed and ring opening of the presumed cyclic phosphate group gave an approximately equimolar mixture of 2- and l-3-glycerophosphates. 5. The structures of substances A and B confirm lysolecithin as 1-monoacyl-l-3-glycerylphosphorylcholine.

Acid Phosphatase↗
PubMed1989

Evidence of a pH-dependent conformational change at the active site of lysolecithin:lysolecithin acyltransferase from rabbit lung.

It has been shown that both activities, hydrolysis and transacylation, of lysolecithin:lysolecithin acyltransferase, as well as the conformation of the polypeptide are critically dependent on a pK around 5.8, but the question remains if the same residue(s) is responsible for the conformational change and the loss of activity. In this paper, ultrasonic cavitation is used to study the pH-dependent inactivation. The results show that there are two first-order inactivation constants which depend on pH and that the transition between them has a pK of 5.9. As the constants of ultrasonic inactivation are very dependent on the accessibility of the residues it is concluded that the conformational change modifies the accessibility of the active site.

1-Acylglycerophosphocholine O-Acyltransferase↗