Action of phospholipases on the phosphatidylcholine exchange protein from beef liver.

The phospholipases A2, C and D have been used to investigate the localization of phosphatidylcholine in the phosphatidylcholine exchange protein from beef liver. The rate of enzymatic hydrolysis of the protein-bound phosphatidylcholine was found to be very low. Addition of deoxycholate, isobutanol or dioxane to the native protein, under conditions where delipidation did not occur, greatly enhanced the hydrolytic action of the phospholipases. From these results it is concluded that phosphatidylcholine may be buried in the protein molecule.     

Action of phospholipases A2 on phosphatidylcholine bilayers. Effects of the phase transition, bilayer curvature and structural defects

We examined the action of porcine pancreatic and bee-venom phospholipase A2 towards bilayers of phosphatidylcholine as a function of several physical characteristics of the lipid-water interface. 1. Unsonicated liposomes of dimyristoyl phosphatidylcholine are degraded by both phospholipases in the temperature region of the phase transition only (cf. Op den Kamp et al. (1974) Biochim. Biophys. Acta 345, 253--256 and Op den Kamp et al. (1975) Biochim. Biophys. Acta 406, 169--177). With sonicates the temperature range in which hydrolysis occurs is much wider. This discrepancy between liposomes and sonicates cannot be ascribed entirely to differences in available substrate surface. 2. Below the phase-transition temperature the phospholipases degrade dimyristoyl phosphatidylcholine single-bilayer vesicles with a strongly curved surface much more effectively than larger single-bilayer vesicles with a relatively low degree of curvature. 3. Vesicles composed of egg phosphatidylcholine can be degraded by pancreatic phospholipase A2 at 37 degrees C, provided that the substrate bilayer is strongly curved. The bee-venom enzyme shows a similar, but less pronounced, preference for small substrate vesicles. 4. In a limited temperature region just above the transition temperature of the substrate the action of both phospholipases initially proceeds with a gradually increasing velocity. This stimulation is presumably due to an increase of the transition temperature, effectuated by the products of the phospholipase action. 5. Structural defects in the substrate bilayer, introduced by sonication below the phase-transition temperature (cf. Lawaczeck et al. (1976) Biochim. Biophys. Acta 443, 313--330) facilitate the action of both phospholipases. The results lead to the general conclusion that structural irregularities in the packing of the substrate molecules facilitate the action of phospholipases A2 on phosphatidylcholine bilayers. Within the phase transition and with bilayers containing structural defects these irregularities represent boundaries between separate lipid domains. The stimulatory effect of strong bilayer curvature can be ascribed to an overall perturbation of the lipid packing as well as to a change in the phase-transition temperature.     

Mechanism of inhibition of adenylate cyclase by phospholipase C-catalyzed hydrolysis of phosphatidylcholine. Involvement of a pertussis toxin-sensitive G protein and protein kinase C.

The phospholipase C-mediated hydrolysis of phosphatidylcholine has been shown recently to be activated by a number of agonists. Muscarinic receptors, which trigger various signal transduction mechanisms including inhibition of adenylate cyclase through Gi, have been shown to be potent stimulants of this novel phospholipid degradative pathway. We demonstrate here, by exogenous addition of Bacillus cereus phosphatidylcholine-hydrolyzing phospholipase C, that phosphatidylcholine breakdown mimics the ability of carbachol to inhibit adenylate cyclase. This effect is sensitive to pertussis toxin and is entirely dependent on the presence of protein kinase C. This kinase is also required for the inhibition by carbachol of adenylate cyclase. These results suggest that the activation of phosphatidylcholine breakdown by phospholipase C may play an important role linking or favoring the coupling muscarinic receptors to Gi. Results presented here also show that phospholipase C-mediated hydrolysis of phosphoinositides by exogenous addition of Bacillus thuringiensis phosphoinositide-hydrolyzing phospholipase C does not affect adenylate cyclase, despite the fact that protein kinase C is translocated to an extent similar to that produced by the hydrolysis of phosphatidylcholine. According to the results shown here, both phospholipases also differ in their ability to down-regulate protein kinase C as well as to phosphorylate p80 and to transmodulate the binding of epidermal growth factor, two well established effects of protein kinase C in Swiss 3T3 fibroblasts. This emphasizes the complexity, from a functional point of view, of protein kinase C activation "in vivo."     

蛋白激酶C研究的最新进展

作为能使蛋白激酶C(PKC)活化的第二信使甘油二酯(DAG)不仅可由磷脂酰肌醇(PtdIns)水解产生,大量实验表明还可从磷脂酰胆碱(PC)水解而来,其中磷脂酶C(PLC)及磷脂酶D(PLD)参与了这一过程,磷脂酶A₂(PLA₂)的作用产物脂肪酸(FA)也能激活PKC.PKC至少有10种亚型,依据其活化方式可分三大类:典型PKC,新PKC和非典型PKC.PKC参与了基因表达的调控.     

The C(27)-steroid hormones calcitriol and ecdysterone in the early phase of its action activates hydrolysis of phosphatidylcholines in target animal tissues]

We have examined in vivo the capacities of two C27-steroid hormones--phytoecdysteroid ecdysterone (20-hydroxyecdysone, 10(-8)M) and calcitriol (1 alpha, 25-dihydroxyvitamin D3, 10(-12)M), as a modulators of phosphatidylcholine hydrolysis in the brain and heart cells of rats. Sever lines of evidence indicate that both hormones may acts as positive regulators of membrane phosphatidylcholine hydrolysis by phospholipases A2, C and D in early (0.5-30 min) membrane phase of its actions, yielding known lipid second messengers (diacylglycerol, phosphatidic acid) and soluble products, that may acts as second messengers (choline,choline phosphate, glycerophosphocholine).     

Modulation of the organization of erythrocyte membrane phospholipids by cytoplasmic ATP. The susceptibility of isoionic human erythrocyte ghosts to attack by detergents and phospholipase C

Human erythrocyte ghosts were prepared in media of physiological ionic composition, and these “isoionic” ghosts were then lysed and resealed in media of varying Ca²⁺, Mg²⁺ and ATP concentrations. The susceptibilities of these ghosts to limited attack by various detergents and by phospholipases C were then compared with the susceptibilities of intact cells to similar attack: attack was assessed by measurements of lysis and of phospholipid hydrolysis. Ghosts were more readily attacked than cells by anionic detergents (cholate, glycocholate, dodecyl sulphate) and by phospholipases C, but Triton X-100 and cetyltrimethylammonium attacked cells and ghosts to the same extent. Mg · ATP^2? partially protected ghosts from attack by the anionic detergents and by the phospholipases C of Bacillus cereus and of Clostridium perfringens. Protection by Mg · ATP^2? occurred only if Mg · ATP^2? had access to the cytoplasmic surface of the membrane. Adenylyl(β-γ-methylene)diphosphonate, a non-hydrolysable ATP analogue, protected as effectively as did Mg · ATP^2?. Internal Mg · ATP^2? caused a marked reduction in the hydrolysis by phospholipases of phosphatidylethanolamine and sphingomyelin, but had no appreciable effect upon the simultaneous hydrolysis of phosphatidylcholine. It therefore seems that interaction of ATP with sites on the cytoplasmic surface of the erythrocyte membrane can, without ATP hydrolysis, cause changes in the organization of the outer surface of the membrane that specifically render phosphatidylethanolamine and sphingomyelin less accessible to attack by extracellular phospholipases.     

Cell signalling through phospholipid breakdown

There is much evidence that G-proteins transduce the signal from receptors for Ca²⁺-mobilizing agonists to the phospholipase C that catalyzes the hydrolysis of phosphoinositides. However, the specific G-proteins involved have not been identified. We have recently purified a 42 kDa protein from liver that activates phosphoinositide phospholipase C and cross-reacts with antisera to a peptide common to G-protein -subunits. It is proposed that this protein is the a-subunit of the G-protein that regulates the phospholipase in this tissue.Ca²⁺-mobilizing agonists and certain growth factors also promote the hydrolysis of phosphatidylcholine through the activation of phospholipases C and D in many cell types. This yields a larger amount of diacylglycerol for a longer time than does the hydrolysis of inositol phospholipids. Consequently phosphatidylcholine breakdown is probably a major factor in long-term regulation of protein kinase C. The functions of phosphatidic acid produced by phospholipase D are speculative, but there is evidence that it is a major source of diacylglycerol in many cell types. The regulation of phosphatidylcholine phospholipases is multiple and involves direct activation by G-proteins, and regulation by Ca²⁺ protein kinase C and perhaps growth factor receptor tyrosine kinases.     

Lipid asymmetry in rabbit small intestinal brush border membrane as probed by an intrinsic phospholipid exchange protein.

All classes of phospholipids present in brush border membrane are exchanged in a 1:1 ratio for egg phosphatidylcholine when brush border membrane vesicles from rabbit small intestine are incubated with small unilamellar vesicles of egg phosphatidylcholine. The exchange reaction exhibits biphasic kinetics similar to those of the hydrolysis of brush border membrane phospholipids by phospholipase A2 and sphingomyelinase C. In both reactions there is an initial fast phase followed by a markedly slower one. The phospholipid exchange appears to be catalyzed by intrinsic brush border membrane protein(s), while the digestion by phospholipases is mediated by externally added enzymes. From a comparison of the kinetics of phospholipid exchange and phospholipid hydrolysis, the following conclusions can be drawn: Both sets of experiments indicate the presence of two phospholipid pools differing in the rate of phospholipid exchange and hydrolysis. Except for sphingomyelin, the size of the two phospholipid pools derived from phospholipid exchange is in good agreement with that derived from phospholipid hydrolysis. This is the main finding of this work, and on the basis of this result the two lipid pools are tentatively assigned to phospholipid molecules located on the outer and inner layer of the brush border membrane. The slow rate of phospholipid exchange reflects the rate of transverse or flip-flop movement of phospholipids. The half-time of this motion is approximately 8 h for isoelectric (neutral) phospholipids such as phosphatidylethanolamine and approximately 80 h for negatively charged phosphatidylserine and phosphatidylinositol. Isoelectric phospholipids (phosphatidylcholine, phosphatidylethanolamine) are preferentially located on the inner (cytoplasmic) side (to about 70%) while the negatively charged phospholipids are more evenly distributed: 55-60% are located on the inner side.     

Hydrolysis of 1-palmitoyl-2-[6-(pyren-1-yl)]hexanoyl-sn-glycero- 3-phospholipids by phospholipase A2: effect of the polar head-group

The effect of the phospholipid polar head-group on the porcine pancreatic phospholipase A2 (phosphatidylcholine 2-acylhydrolase, EC 3.1.1.4) reaction was studied using 1-palmitoyl-2-[6-(pyren-1-yl)]hexanoyl-sn-glycero-3- phosphatidylcholine, -ethanolamine, -glycerol, -monomethylester and -serine as substrates. Except for the monomethylester analogue, which was maximally activated by 3.5 mM CaCl2, maximal enhancement of hydrolysis of the other pyrenephospholipids was obtained at 2 mM Ca2+. Sodium cholate inhibited hydrolysis of the ethanolamine and serine lipids, whereas a slight (1.4-2.0-fold) activation was observed for the -choline, -glycerol and -monomethylester derivatives. Arrhenius plots of hydrolysis of pyrenephospholipids by porcine pancreatic phospholipase A2 revealed no discontinuities, thus indicating the absence of phase transition for these lipids in the temperature range 15-45 degrees C. Specific activities of porcine and bovine pancreatic, porcine intestinal and snake venom (Crotalus atrox) phospholipases A2 towards pyrenephospholipid liposomes were then compared. Whereas the snake venom phospholipase A2 preferred phosphatidylcholine as a substrate, the other phospholipases A2 preferred acidic phospholipids in the order monomethylester greater than or equal to glycerol greater than or equal to serine.     

Phospholipase A1 acting on phosphatidic acid in porcine platelet membranes

1-[14C]Palmitoyl-2-[3H]arachidonoyl-sn-glycerol 3-phosphate was hydrolyzed to form [14C]palmitic acid and 2-[3H]arachidonoyl-glycerophosphate by porcine platelet membranes. This phospholipase A1 activity was relatively specific for phosphatidic acid; the addition of several other phospholipids in equimolar amounts did not have a significant effect on the hydrolysis of radiolabeled phosphatidic acid, and the specific activity for phosphatidic acid hydrolysis was 20-fold higher than that of the hydrolysis of phosphatidylcholine, phosphatidylethanolamine, or phosphatidylinositol under the conditions used. This phospholipase A1 acting on phosphatidic acid has properties different from those reported for other phospholipases and lipases present in platelets.     

Specificity of phospholipases in methylcholanthrene-transformed mouse fibroblasts activated by bradykinin, thrombin, serum, and ionophore A23187.

Methylcholanthrene-transformed mouse fibroblasts synthesize prostaglandins in response to bradykinin, thrombin, serum, and the ionophore A23187. These agents activate phospholipases, thereby releasing fatty acids from phospholipids. To examine the phospholipid specificity of the phospholipases activated by bradykinin, thrombin, serum, and A23187, cells were labeled with [14C]arachidonic acid and stimulated with these agents in the presence of delipidated bovine serum albumin. Phospholipid classes were resolved by two-dimensional chromatography on silica gel-coated paper. Only phosphatidylinositol and phosphatidylcholine lost radioactivity upon stimulation. To characterize the fatty acid specificity of the phospholipases, cells were incubated with 14C-labeled stearic, oleic, linoleic, eicosatrienoic, or arachidonic acid and then exposed to the stimuli. Bradykinin, thrombin, and serum caused specific release of radioactivity into the medium only from cells labeled with arachidonic acid or eicosatrienoic acid, whereas A23187 caused release from cells labeled with any one of the five fatty acids. We conclude that bradykinin, thrombin, and serum activate phospholipases that specifically hydrolyze arachidonyl and eicosatrienoyl phosphatidylinositol and phosphatidylcholine, whereas A23187 is less specific activator of phospholipases.     

Phospholipase A2 as a probe of phospholipid distribution in erythrocyte membranes. Factors influencing the apparent specificity of the reaction.

The action of snake venom phospholipases A2 in intact human erythrocytes was investigated in detail. The basis phospholipase from Agkistrodon halys blomhifii was found to induce both hydrolysis of membrane phospholipids and total cell hemolysis under certain experimental conditions. The hydrolytic action of the basic enzyme was found to consist of two sequential events: (a) hydrolysis of 70% of the total cell ph osphatidylcholine without any evident hemolysis; and (b) complete hydrolysis of the remaining phosphatidylcholine, followed closely by extensive phosphatidylethanolamine hydrolysis and finally with onset of hemolysis, attack on the phosphatidylserine. At pH 7.4 and 10 mM Ca2+ only stage (a) occurred. However, a slight elevation of the pH of incubation to pH 8.0 and/or inclusion of 40 mM Ca2+ in the reaction mixture caused both events (a) and (b) to occur. The addition of glucose limited the action of the enzyme to stage (a) under any reaction conditions. An investigation showed that enzymically induced hemolysis occurred under conditions where the intracellular ATP levels were lowered. Data are presented which suggest that stage (b) is mediated by in influx of Ca2+ into the cell when the levels of ATP are low. Interestingly the phosphllipase from Naja naja venom (Pakistan) yielded results similar to those observed with the basic enzyme from Agkistrodon venom. However, the enzyme from Crotalus adamanteus and the acidic enzyme also present in the Agkistrodon venom produced only slight hydrolysis or hemolysis under any of the conditions studied. Other species of erythrocytes, e.g., guinea pig, monkey, pig, and rat, were tested but only those from guinea pig behaved similarly to the human cells. Pig, monkey, and rat erythrocytes underwent very limited hydrolysis and hemolysis. It is evident that the use of these phospholipases to probe the localization of phospholipds in erythrocyte membranes must be approached with caution. Certain facets of this problem are discussed.     

Hydrolysis of 1-palmitoyl-2-[6-(pyren-1-yl)]hexanoyl-sn-glycero-3-phospholipids by phospholipase A2: effect of the polar head-group

The effect of the phospholipid polar head-group on the porcine pancreatic phospholipase A₂ (phosphatidylcholine 2-acylhydrolase, EC 3.1.1.4) reaction was studied using 1-palmitoyl-2-[6-(pyren-1-yl)]hexanoyl-sn-glycero-3-phosphatidylcholine,-ethanolamine, -glycerol, -monomethylester and -serine as substrates. Except for the monomethylester analogue, which was maximally activated by 3.5 mM CaCl₂, maximal enhancement of hydrolysis of the other pyrenephospholipids was obtained at 2 mM Ca₂₊. Sodium cholate inhibited hydrolysis of the ethanolamine and serine lipids, whereas a slight (1.4–2.0-fold) activation was observed for the -choline, -glycerol and -monomethylester derivatives. Arrhenius plots of hydrolysis of pyrenephospholipids by porcine pancreatic phospholipase A₂ revealed no discontinuities, thus indicating the absence of phase transition for these lipids in the temperature range 15–45°C. Specific activities of porcine and bovine pancreatic, porcine intestinal and snake venom (Crotalus atrox) phospholipases A₂ towards pyrenephospholipid liposomes were then compared. Whereas the snake venom phospholipase A₂ preferred phosphatidylcholine as a substrate, the other phospholipases A₂ preferred acidic phospholipids in the order monomethylester ⩾ glycerol ⩾ serine.     

The hydrolysis of monolayers of phosphatidyl-[Me-14C]choline by phospholipase D

1. The hydrolysis of monolayers of phosphatidyl[Me-(14)C]choline at the air/water interface by phospholipase D (phosphatidylcholine phosphatidohydrolase) was investigated by a surface-radioactivity technique by using a flow counter. 2. Phosphatidylcholine of high specific radioactivity was prepared biosynthetically in good yield from [Me-(14)C]choline by using Saccharomyces cerevisiae. 3. At initial monolayer pressures between 12 and 25 dynes/cm. the hydrolysis occurred in two stages, an initial slow hydrolysis followed by a rapid hydrolysis. Below 3dynes/cm. and above 28dynes/cm. no enzymic hydrolysis of pure phosphatidylcholine monolayers could be detected. 4. The rapid hydrolysis was proportional to the enzyme concentration in the subphase, its pH optimum was 6.6, and 0.2mm-Ca(2+) was required for maximal activity. 5. Hydrolysis of the film was accompanied by a pronounced fall in the surface pressure even though the phosphatidic acid formed did not leave the film. When the pressure fell to low values the hydrolysis ceased even if the film was only partially hydrolysed. 6. Above monolayer pressures of 28dynes/cm. enzymic hydrolysis could be initiated by inclusion of phosphatidic acid (and less effectively stearyl hydrogen sulphate) in the film, although the rates were not appreciably higher than those observed at 25dynes/cm. with a pure phosphatidylcholine film. 7. The initiation of the hydrolysis by phosphatidic acid was facilitated by the inclusion of high Ca(2+) concentrations and certain carboxylic acid buffer anions in the subphase, although these did not activate by themselves. 8. The initiation of the hydrolysis at high pressures could not be related to any change in the surface potential brought about by the addition of the long-chain anions to the film, nor could it be ascribed to a surface dilution effect. 9. The results are discussed in relation to previous studies on the hydrolysis of phosphatidylcholine particles by the enzyme and also similar investigations on phosphatidylcholine monolayers with other phospholipases.     

Regulation of sphingomyelinase and phospholipase C activity in liver cell membranes of rats of different ages

The changes in the functional activities of sphingomyelinase and phospholipase C from rat liver cell plasma membranes were studied in postnatal ontogenesis in the presence of thyroxin and mercasolyl. It was found that endogenous phospholipases of plasma membranes control of phospholipid content in rat liver cells. The sphingomyelinase activity is under control of thyroid hormones, whereas that of phospholipase C which is phosphatidyl choline-specific, is unaffected by them. The data obtained testify to the possible involvement of diacylglycerols formed via enzymatic hydrolysis of phosphatidylcholine, in the regulation of the sphingomyelinase activity.     

Diacylglycerol potentiates phospholipase attack upon phospholipid bilayers: possible connection with cell stimulation

Many phospholipases of the A or C types show a very limited ability to hydrolyse phospholipids such as phosphatidylcholine or phosphatidylinositol which adopt a bilayer form when hydrated. The addition of unsaturated 1,2 or 1,3 diacylglycerols to such substances produces a marked stimulation of the attack. In contrast, the hydrolysis of phosphatidylethanolamine, which normally exists in the hexagonal II structure, is not stimulated by diacylglycerol. It is suggested that the liberation of diacylglycerol which often occurs during cell stimulation, may play a part in activating the associated cascade of phospholipid reactions.     

Pancreatic porcine phospholipase A2 catalyzed hydrolysis of phosphatidylcholine in lecithin-bile salt mixed micelles: kinetic studies in a lecithin-sodium cholate system

Pancreatic porcine phospholipase A2 catalyzed hydrolysis of phosphatidylcholine in bile salt lecithin mixed micelles has been studied, utilizing a series of assay mixtures for which the micellar size, weight, and composition had been experimentally determined. Under these conditions the enzymatic hydrolysis is dependent on the phosphatidylcholine-to-sodium cholate molar ratio within the mixed micelle rather than the bulk concentration of the phospholipid in the mixture: at 5 mM phosphatidylcholine, variation of the NPC/NNaCh ratio from 0.2 to 2.0 increases the enzymatic activity from 82 to 933 mumol/min/mg protein. The initial rates are linear throughout the entire series of assay mixtures, the activity vs micellar concentration curves exhibit saturation behavior, and treatment of the data according to the "surface-as-cofactor" theory provides linear double-reciprocal plots which intersect in one point. The assay system should be applicable for detailed kinetic studies of lipolytic enzymes, including mammalian phospholipases which exhibit rather low activities toward lecithin-Triton X-100 mixed micelles. The system should also provide a convenient basis for mechanistic studies involving the use of inhibitory phospholipid substrate analogs.     

Bacterial phospholipases C.

A variety of pathogenic bacteria produce phospholipases C, and since the discovery in 1944 that a bacterial toxin (Clostridium perfringens alpha-toxin) possessed an enzymatic activity, there has been considerable interest in this class of proteins. Initial speculation that all phospholipases C would have lethal properties has not been substantiated. Most of the characterized enzymes fall into one of four groups of structurally related proteins: the zinc-metallophospholipases C, the sphingomyelinases, the phosphatidylinositol-hydrolyzing enzymes, and the pseudomonad phospholipases C. The zinc-metallophospholipases C have been most intensively studied, and lethal toxins within this group possess an additional domain. The toxic phospholipases C can interact with eukaryotic cell membranes and hydrolyze phosphatidylcholine and sphingomyelin, leading to cell lysis. However, measurement of the cytolytic potential or lethality of phospholipases C may not accurately indicate their roles in the pathogenesis of disease. Subcytolytic concentrations of phospholipase C can perturb host cells by activating the arachidonic acid cascade or protein kinase C. Nonlethal phospholipases C, such as the Listeria monocytogenes PLC-A, appear to enhance the release of the organism from the host cell phagosome. Since some phospholipases C play important roles in the pathogenesis of disease, they could form components of vaccines. A greater understanding of the modes of action and structure-function relationships of phospholipases C will facilitate the interpretation of studies in which these enzymes are used as membrane probes and will enhance the use of these proteins as models for eukaryotic phospholipases C.     

Bacterial phospholipases C.

A variety of pathogenic bacteria produce phospholipases C, and since the discovery in 1944 that a bacterial toxin (Clostridium perfringens alpha-toxin) possessed an enzymatic activity, there has been considerable interest in this class of proteins. Initial speculation that all phospholipases C would have lethal properties has not been substantiated. Most of the characterized enzymes fall into one of four groups of structurally related proteins: the zinc-metallophospholipases C, the sphingomyelinases, the phosphatidylinositol-hydrolyzing enzymes, and the pseudomonad phospholipases C. The zinc-metallophospholipases C have been most intensively studied, and lethal toxins within this group possess an additional domain. The toxic phospholipases C can interact with eukaryotic cell membranes and hydrolyze phosphatidylcholine and sphingomyelin, leading to cell lysis. However, measurement of the cytolytic potential or lethality of phospholipases C may not accurately indicate their roles in the pathogenesis of disease. Subcytolytic concentrations of phospholipase C can perturb host cells by activating the arachidonic acid cascade or protein kinase C. Nonlethal phospholipases C, such as the Listeria monocytogenes PLC-A, appear to enhance the release of the organism from the host cell phagosome. Since some phospholipases C play important roles in the pathogenesis of disease, they could form components of vaccines. A greater understanding of the modes of action and structure-function relationships of phospholipases C will facilitate the interpretation of studies in which these enzymes are used as membrane probes and will enhance the use of these proteins as models for eukaryotic phospholipases C.     

Effect of phospholipases A2 from bee and cobra venom on the phospholipid composition and Na+-,K+-ATPase activity of synaptosomes

The bee and cobra venom phospholipases A2 as well as partially acetylated cobra venom phospholipase A2 are studied for their effect on phospholipid composition of synaptosomes and their Mg2+- and Na+,K+-ATPase activity. It is established that these phospholipases induce the splitting of phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine, inhibition of the Na+,K+-ATPase activity and activation of Mg2+-ATPase. Bee venom phospholipase A2 is more effective than cobra venom phospholipase A2, the both phospholipases splitting phosphatidylethanolamine most intensively. The ATPase activity may be partially or completely restored by exogenic phosphatidylcholine and phosphatidylserine; exogenic phosphatidylethanolamine is not efficient in this respect.