Effects of antimalarial drugs on phospholipase A and lysophospholipase activities in plasma membrane, mitochondrial, microsomal and cytosolic subcellular fractions of rat liver

Activities of membrane-associated phospholipases A1 and A2, and membrane-associated as well as soluble lysophospholipases were measured in different subcellular fractions of rat liver, using suspensions of stereospecifically labelled radioactive phospholipids as substrates. Plasma membranes and endoplasmic reticulum were shown to contain phospholipase A1 and lysophospholipase activities, both of which could be stimulated by Ca2+, mitochondria Ca2+-dependent phospholipase A2 and cytosol Ca2+-independent lysophospholipase activities. Each of these lipolytic enzymes could be inhibited by antimalarial drugs (chloroquine, mepacrine, primaquine) at concentrations above 1 x 10(-4) M. Inhibition of the alkaline cytosolic lysophospholipase by these drugs was noncompetitive with respect to the substrate, and the inhibitory potency increased, when the pH was raised.     

Isolation and characterization of three lysophospholipases from the murine macrophage cell line WEHI 265.1.

Anion exchange chromatography of WEHI 265.1 cell homogenates resolved the lysophospholipase activity into three peaks, when assayed using lysophosphatidylcholine as a substrate. Peaks 1 and 2 were purified by sequential hydrophobic interaction and gel filtration chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified peaks 1 and 2 indicated homogeneous proteins with apparent masses of 28 and 27 kDa, respectively. Peak 3 lysophospholipases was partially purified by hydrophobic, hydroxyapatite and gel filtration chromatography. Peak 3 lysophospholipase also had calcium-dependent phospholipase A2 activity, which further co-purified with the lysophospholipase activity. The three lysophospholipases were characterized with respect to substrate specificity, additional enzymatic activities and the effects of lipids, metal ions and other compounds on enzymatic activity. Peaks 1, 2 and 3 hydrolyzed lysophosphatidylcholine most readily, but lysophosphatidylethanolamine also served as substrate for each enzyme. Furthermore, all three enzymes hydrolyzed platelet activating factor and acetylated lysophosphatidylcholine. Each lysophospholipase was inhibited by free fatty acids and by palmitoyl carnitine, although the relative sensitivities to these agents differed among the enzymes. The lysophospholipase activities of peaks 1 and 2, but not peak 3, were inhibited by phenylmethylsulfonyl fluoride, diisopropyl fluorophosphate and N-ethylmaleimide. Although they had similar masses, the amino acid compositions of peaks 1 and 2 differed, indicating that these are distinct proteins rather than posttranslational modifications of the same gene product.     

Isolation and properties of lysophospholipases from the venom of an Australian elapid snake, Pseudechis australis.

Two lysophospholipases were isolated from the venom of an Australian elapid snake (subfamily Acanthophiinae), Pseudechis australis, by sequential chromatography on CM-52 cellulose, Sephadex G-75 and DE-52 cellulose columns. They were very similar to each other. One of them, lysophospholipase I, was obtained as a homodimer, the monomer of which consisted of 123 amino acid residues with seven disulphide bridges. The amino acid composition and the N-terminal amino acid sequence of the enzyme were similar to those of phospholipase A2, Ca2+ was required for its activity and the maximum activity was attained at 2 mM-CaCl2 in the presence of 1 mM-EDTA. The optimum pH was 7.5. Lysophospholipase I hydrolysed lysophosphatidylcholine more rapidly than lysophosphatidylethanolamine. It did not hydrolyse, however, phosphatidylcholine, 1-palmitoylglycerol, tripalmitoylglycerol or p-nitrophenyl acetate. Modification of the enzyme with p-bromophenacyl bromide or 2-nitrophenylsulphenyl chloride suppressed the activity. A strong direct haemolytic activity was exhibited when the lysophospholipase was present together with phospholipase A2.     

Orientotoxin--a new presynaptic neurotoxin from the venom of the giant hornet Vespa orientalis

Orientotoxin, a novel presynaptically acting neurotoxin from the venom of giant hornet Vespa orientalis, has been isolated by gel filtration and ion exchange chromatography and characterized. The toxin has a molecular mass of 18,000. Highly purified preparations of orientotoxin possessed clearly manifested lysophospholipase activity and can block both induced and spontaneous release of neurotransmitter from the presynaptic nerve membrane.     

Hemolytic potency and phospholipase activity of some bee and wasp venoms

1. The action of crude venoms of four aculeate species: Apis mellifera, Vespa crabro, Vespula germanica and Vespula vulgaris on human erythrocytes was investigated in order to determine the lytic and phospholipase activity of different aculeate venoms and their ability to induce red blood cell hemolysis. 2. Bee venom was the only extract to completely lyse red blood cells at the concentration of 2-3 micrograms/ml. 3. Phospholipase activity in all of the examined vespid venoms was similar and the highest value was recorded in V. germanica. 4. Vespid venoms exhibited phospholipase B activity, which is lacking in honeybee venom. 5. In all membrane phospholipids but lecithin, lysophospholipase activity of vespid venoms was 2-6 times lower than the relevant phospholipase activity. 6. The incubation of red blood cells with purified bee venom phospholipase A2 was not accompanied by lysis and, when supplemented with purified melittin, the increase of red blood cell lysis was approximately 30%.     

Amino acid sequence of orientotoxins I and II from the venom of the hornet Vespa orientalis

Orientotoxin I, a neurotoxin of presynaptic effect having a lysophospholipase activity, and orientotoxin II, a highly toxic phospholipase A2, were isolated from the hornet Vespa orientalis venom, and their primary structures were determined. Despite their different functional activity, orientotoxin I and II proved to be structural homologues, differing significantly in the amino acid sequence from well-known toxic phospholipase from other sources.     

Protein allergens of white-faced hornet, yellow hornet, and yellow jacket venoms.

White-faced hornet, yellow hornet, and yellow jacket venoms have very similar protein compositions; each contains mainly three basic proteins. Two of these proteins have hyaluronidase and phospholipase activities and the third one, designated as antigen 5, is of as yet unidentified biochemical function. These three proteins have molecular weights of about 45 000, 35 000, and 25 000, respectively. The three proteins of white-faced hornet venom have been purified to near homogeneity, while this is the case only for antigen 5 of yellow hornet and yellow jacket venoms. Strong antigenic cross-reaction of the hyaluronidase from these three vespid venoms was observed using specific rabbit anti-venom sera, while weak cross-reactions of phospholipases and of antigen 5s were observed. All three proteins are active as allergens to varying degrees in vespid sensitive individuals. With each vespid venom its antigen 5 seems to be the major allergen. The results help to clarify the commonly observed varying degrees of multiple sensitivity of people to different vespids.     

Properties of the Group IV phospholipase A2 family

The Group IV phospholipase A₂ family is comprised of six intracellular enzymes commonly called cytosolic phospholipase A₂ (cPLA₂) , cPLA₂β, cPLA₂γ, cPLA₂δ, cPLA₂ε and cPLA₂ζ. They are most homologous to phospholipase A and phospholipase B/lysophospholipases of filamentous fungi particularly in regions containing conserved residues involved in catalysis. However, a number of other serine acylhydrolases (patatin, Group VI PLA₂s, Pseudomonas aeruginosa ExoU and NTE) contain the Ser/Asp catalytic dyad characteristic of Group IV PLA₂s, and recent structural analysis of patatin has confirmed its structural similarity to cPLA₂. A characteristic of all these serine acylhydrolases is their ability to carry out multiple reactions to varying degrees (PLA₂, PLA₁, lysophospholipase and transacylase activities). cPLA₂, the most extensively studied Group IV PLA₂, is widely expressed in mammalian cells and mediates the production of functionally diverse lipid products in response to extracellular stimuli. It has PLA₂ and lysophospholipase activities and is the only PLA₂ that has specificity for phospholipid substrates containing arachidonic acid. Because of its role in initiating agonist-induced release of arachidonic acid for the production of eicosanoids, cPLA₂ activation is important in regulating normal and pathological processes in a variety of tissues. Current information available about the biochemical properties and tissue distribution of other Group IV PLA₂s suggests they may have distinct mechanisms of regulation and functional roles.     

The effect of calmodulin and chlorpromazine on the activity of phospholipases A2 from various sources

The effects of calmodulin and chlorpromazine on purified phospholipase A2 preparations from snake venoms: cobra (Naja naja oxiana), echis (Ehis multisquamatus) and Agkistrodon halys halys, as well as on phospholipases A2 from rat liver mitochondria and human platelets were studied. It was shown that within the concentration range of 1-5 microM calmodulin stimulates the phospholipase activity. Chlorpromazine inhibits the activity of these enzymes, the degree of inhibition being different for various phospholipases. Calmodulin was shown to interact with the phospholipases in the absence of exogenous Ca2+. The results obtained indicate that all phospholipases tested are calmodulin-dependent enzymes.     

Hemolytic effect of phospholipase A2 and orientotoxin from venom of the great hornet, Vespa orientalis

The effect of toxic phospholipase A2 and orientotoxin from the venom of the giant hornet Vespa orientalis on human erythrocytes was studied. It was shown that these venom components are potent hemolytic agents, the efficiency of the latter being by about two orders of magnitude as high as that of phospholipase A2. The hemolytic function of the both components is enhanced in the presence of low concentrations of Ca2+, whereas high concentrations of this cation exert an inhibiting action. Polyvalent cations, in particular, ruthenium red, peptide HR-1, mellitin and cytotoxins Us-1 and Us-5 synergetically increase the hemolytic effect of phospholipase A2. During erythrocyte hemolysis the synergistic effect is manifested upon a combined action of phospholipase A2 and orientotoxin. The combination of these toxins increases the total hemolytic activity and produces a far greater effect than in could be expected in the case of each of these compounds taken separately.     

Lysophospholipase activity in cell-wall fragments contaminating mitochondrial fractions of Neurospora crassa.

Crude mitochondrial preparations from Neurospora crassa contain high levels of lysophospholipase (EC 3.1.1.5) activity when assayed with lysophosphatidylcholine as a substrate. In mitochondria purified by centrifugation on a sucrose-density gradient this activity is virtually absent. The enzyme was shown to be linked to a contaminating cell fraction which mainly consists of cell-wall material as was demonstrated by electron microscopy and chemical analysis. The enzyme has no absolute Ca2+ requirement but it is slightly stimulated by 10 mM CaCl2. The pH optimum is 5.8 in presence of CaCl2 and is shifted to 4.2 when EDTA is present. In contrast to other lysophospholipases this enzyme is only slightly inhibited by deoxycholate. This detergent is able to release part of the lysophospholipase activity from the wall fragments without producing an increase in specific activity. The enzyme is possibly secreted by the cells as high lysophospholipase activities were also found in the culture medium.     

Partial purification of a lipolytic enzyme from Escherichia coli.

An enzyme with phospholipase Al activity was purified some 500-fold from Escherichia coli cell homogenates. Lipase, phospholipase A2, and lysophospholipase copurified with phospholipase A1 and the four activities displayed similar susceptibility to heat treatment. The phospholipase A and lipase activities were recovered in a single band when partially purified preparations were subjected to SDS gel electrophoresis. Phospholipase, lysophospholipase, and lipase all required Ca2+ for activity. Phosphatidylcholine, phosphatidylethanolamine, and their lyso analogues were all hydrolysed at equivalent rates and these were substantially greater than the rate of methylpalmitate or tripalmitoylglycerol hydrolyses under similar incubation conditions. Evidence for a direct but slow hydrolysis of the ester at position 2 of phosphoglyceride was obtained; however, release of fatty acid from this position is mostly indirect involving acyl migration to position 1 and subsequent release of the translocated fatty acid. Escherichia coli, therefore, appears to possess a lipolytic enzyme of broad substrate specificity acting mainly at position 1 but also at position 2 of phosphoglycerides and on triacylglycerols and methyl fatty-acid esters.     

The stimulation by transmitter substances and putative transmitter substances of the net activity of phospholipase A2 of synaptic membranes of cortex of guinea-pig brain.

1. The distribution of the hydrolyses of phosphatidylcholine by phospholipase A2 and phospholipase A1, and the hydrolysis of lysophosphatidylcholine by lysophospholipase, in subcellular and subsynaptosomal fractions of cerebral cortices of guinea-pig brain, was determined. 2. Noradrenaline stimulated hydrolysis by phospholipase A2 in whole synaptosomes, synaptic membranes and fractions containing synaptic vesicles. 3. Stimulation of hydrolysis by phospholipase A2 in synaptic membranes by noradrenaline was enhanced by CaCl2, and by a mixture of ATP and MgCl2. The optimum concentration of CaCl2, in the presence of ATP and MgCl2, for stimulation by 10 muM-noradrenaline was in the range 1-10muM. The optimum concentration for ATP-2MgCl2 in the presence of 1 muM-CaCl2 was in the range 0.1-1mM. 4. Hydrolysis by phospholipase A2 of synaptic membranes was also stimulated by acetylcholine, carbamoylcholine, 5-hydroxytryptamine, dopamine (3,4-dihydroxyphenethylamine), histamine, psi-aminobutyric acid, glutamic acid and aspartic acid. With appropriate concentrations of cofactors, sigmoidal dose-response curves were obtained, half-maximum stimulations being obtained with concentrations of stimulant in the range 0.1-1muM. 5. Taurine also stimulated hydrolysis of phosphatidylcholine by phospholipase A2. There were only slight stimulations with methylamine, ethylenediamine or spermidine. No stimulation was obtained with glucagon.     

Kinetic properties of a high molecular mass arachidonoyl-hydrolyzing phospholipase A2 that exhibits lysophospholipase activity.

The first step in the production of eicosanoids and platelet-activating factor is the hydrolysis of arachidonic acid from membrane phospholipid by phospholipase A2. We previously purified from the macrophage cell line RAW 264.7 an intracellular phospholipase A2 that preferentially hydrolyzes sn-2-arachidonic acid. The enzyme exhibits a molecular mass of 100 kDa and an isoelectric point of 5.6. When assayed for other activities, the phospholipase A2 was found to exhibit lysophospholipase activity against palmitoyllysoglycerophosphocholine, and both activities copurified to a single band on silver-stained sodium dodecyl sulfate-polyacrylamide gels. An antibody against the macrophage enzyme was found to quantitatively immunoprecipitate both phospholipase A2 and lysophospholipase activities from a crude cytosolic fraction. When the immunoprecipitated material was analyzed on immunoblots, a single band at 100 kDa was evident, further suggesting that a single protein possessed both enzyme activities. When assayed as a function of palmitoyllysoglycerophosphocholine concentration and plotted as a double-reciprocal plot, two different slopes were apparent, corresponding to concentrations above and below the critical micellar concentration (7 microM) of the substrate. Above the critical micellar concentration, lysophospholipase exhibited an apparent Km of 25 microM and a Vmax of 1.5 mumol/min/mg. Calcium was not required for lysophospholipase activity, in contrast to phospholipase A2 activity. The enzyme, when assayed as either a phospholipase A2 or lysophospholipase, exhibited nonlinear kinetics beyond 1-2 min despite low substrate conversion. Readdition to more substrate after the activity plateaued did not result in further enzyme activity, ruling out substrate depletion. Readdition of enzyme, however, resulted in another burst of enzyme activity. The results are not consistent with product inhibition, but suggest that the enzyme may be subject to inactivation during catalysis.     

The PLB2 gene of Saccharomyces cerevisiae confers resistance to lysophosphatidylcholine and encodes a phospholipase B/lysophospholipase

The PLB1 gene of Saccharomyces cerevisiae encodes a protein that demonstrates phospholipase B, lysophospholipase, and transacylase activities. Several genes with significant homology to PLB1 exist in the S. cerevisiae genome, raising the possibility that other proteins may contribute to the total phospholipase B/lysophospholipase/transacylase activities of the cell. We report the isolation of a previously uncharacterized gene that is highly homologous to PLB1 and that, when overexpressed, confers resistance to 1-palmitoyllysophosphatidylcholine. This gene, which is located adjacent to the PLB1 gene on the left arm of chromosome XIII and which we refer to as PLB2, encodes a phospholipase B/lysophospholipase. Unlike PLB1, this gene product does not contain significant transacylase activity. The PLB2 gene product shows lysophospholipase activity toward lysophosphatidylcholine, lysophosphatidylserine, and lysophosphatidylethanolamine. Whereas deletion of either PLB1 or PLB2 resulted in the loss of 80% of cellular lysophospholipase activity, a plb1/plb2 double deletion mutant is completely devoid of lysophospholipase activity toward the preferred substrate lysophosphatidylcholine. Overexpression of PLB2 was associated with an increase in total cellular phospholipase B/lysophospholipase activity, as well as the appearance of significant lysophospholipase activity in the medium. Moreover, overexpression of PLB2 was associated with saturation at a higher cell density, and an increase in total cellular phospholipid content, but no change in phospholipid composition or fatty acid incorporation into cellular lipids. Deletion of PLB2 was not lethal and did not result in alteration of membrane phospholipid composition or content. PLB2 gene expression was found to be maximal during exponential growth conditions and was decreased in late phase, in a manner similar to other genes involved in phospholipid metabolism.     

Charcot-Leyden crystal protein (galectin-10) is not a dual function galectin with lysophospholipase activity but binds a lysophospholipase inhibitor in a novel structural fashion

Charcot-Leyden crystal (CLC) protein, initially reported to possess weak lysophospholipase activity, is still considered to be the eosinophil's lysophospholipase, but it shows no sequence similarities to any known lysophospholipases. In contrast, CLC protein has moderate sequence similarity, conserved genomic organization, and near structural identity to members of the galectin superfamily, and it has been designated galectin-10. To definitively determine whether or not CLC protein is a lysophospholipase, we reassessed its enzymatic activity in peripheral blood eosinophils and an eosinophil myelocyte cell line (AML14.3D10). Antibody affinity chromatography was used to fully deplete CLC protein from eosinophil lysates. The CLC-depleted lysates retained their full lysophospholipase activity, and this activity could be blocked by sulfhydryl group-reactive inhibitors, N-ethylmaleimide and p-chloromercuribenzenesulfonate, previously reported to inhibit the eosinophil enzyme. In contrast, the affinity-purified CLC protein lacked significant lysophospholipase activity. X-ray crystallographic structures of CLC protein in complex with the inhibitors showed that p-chloromercuribenzenesulfonate bound CLC protein via disulfide bonds with Cys(29) and with Cys(57) near the carbohydrate recognition domain (CRD), whereas N-ethylmaleimide bound to the galectin-10 CRD via ring stacking interactions with Trp(72), in a manner highly analogous to mannose binding to this CRD. Antibodies to rat pancreatic lysophospholipase identified a protein in eosinophil and AML14.3D10 cell lysates, comparable in size with human pancreatic lysophospholipase, which co-purifies in small quantities with CLC protein. Ligand blotting of human and murine eosinophil lysates with CLC protein as probe showed that it binds proteins also recognized by antibodies to pancreatic lysophospholipase. Our results definitively show that CLC protein is not one of the eosinophil's lysophospholipases but that it does interact with eosinophil lysophospholipases and known inhibitors of this lipolytic activity.     

Purification and properties of lysophospholipase from the venom of the giant hornet Vespa orientalis

Using biospecific chromatography on polylysocephamide, a toxic phospholipase possessing a presynaptic effect on neuromuscular preparations was isolated from the venom of the giant hornet Vespa orientalis. The enzyme was shown to possess a high hydrolytic activity towards 1-acyllysophosphatidylcholine within a narrow pH range (pH optimum 7.5). The enzyme activity was suppressed by detergents of various chemical composition. Lysophospholipase caused an intensive hemolysis of washed human erythrocytes. The catalytic and hemolytic functions of the enzyme were sensitive to metal ions, however, in a different degree. Ca2+ and Mn2+ activated, while Cu2+ and Zn2+ inhibited the enzyme. Mg2+ and Sr2+ had no effect on the enzyme activity.     

Lysosomal phospholipase A activities of rat ovarian tissue.

1.1. Lysosome-enriched fractions were prepared by differential centrifugation of homogenates of luteinized rats ovaries. Acid phospholipase A activities were characterized with [U-14C]diacyl-sn-glycero-3-phosphocholine and 1-palmitoyl-2-[9,10-3H]- or [1-14C]oleoyl-sn-glycero-3-phosphocholine as substrates. Acid phospholipase A1 activity had properties similar to other hydrolases of lysosomal origin; subcellular distribution, latency and acidic pH optimum. Acid phospholipase A2 activity with similar characteristics was also tentatively identified. We were unable to exclude the possibility that the combined action of phospholipase A1 and lysophospholipase contributed to the release of acyl moieties from the 2-position of the synthetic substrates. 2. Lysophospholipase activity was present in the lysosome-enriched fractions. This activity had an alkaline pH optimum. 3. Phospholipase A1 and A2 activities solubilized from lysosome fractions by freeze-thawing were inhibited by Ca2+ and slightly activated by EDTA. A Ca2+- stimulated phospholipase A2 activity, with an alkaline pH optimum, remained in the particulate residue of freeze-thawed lysosome preparations. This activity is believed to represent mitochondrial contamination. 4. Activities of acid phospholipase A, as well as other acid hydrolases, increased approx. 1.5-fold between 1 and 4 days following induction of luteinizatin, suggesting a hormonal influence on lysosomal enzyme activities.     

Lipolytic enzymes in bovine thyroid tissue. I. Subcellular localization, purification and characterization of acid phospholipase A1.

In mammalian cells the catabolism of membrane phosphoglycerides proceeds probably entirely through a deacylation pathway catalysed by phospholipase A and lysophospholipase (Wise & Elwyn, 1965). In the initial attack of diacylphosphoglycerides by phospholipase A two enzymatic activities with different positional specificities have been distinguished: phospholipase A1 (phosphatidate 1-acyl hydrolase EN 3.1.1.32) and phospholipase A2 (phosphatidate 2-acyl hydrolase EN 3.1.1.4) (Van Deenen & De Haas, 1966). Studies on these intracellular phospholipases were mainly concerned with their subcellular localization. Only occasionally more detailed enzymatic investigations have been conducted on them, in contrast to export phospholipases e.g. from snake venom, bee venom and porcine pancreas, which have been extensively investigated (Brockerhoff & Jensen 1974a). In a previous paper (De Wolf et al., 1976a), the presence of phospholipase A1 and phospholipase A2 activities in bovine thyroid was demonstrated, using 1-[9, 10-3H] stearoyl-2-[1-14C] linoleyl-sn-glycero-3-phosphocholine as a substrate. Optimal activity was observed in both instances at pH 4. Addition of the anionic detergent sodium taurocholate increased the A2 type activity and decreased the A1 type activity suggesting the presence of different enzymes. The lack of influence of Ca2+-ions and EDTA and the acid pH optima could suggest lysosomal localization. In this paper the subcellular distribution of both acid phospholipase activities is described as well as a purification scheme for phospholipase A1. Some characteristics of the purified enzyme preparation are discussed.     

Purification and characterization of a lysophospholipase from a macrophage-like cell line P388D1

Two lysophospholipase activities (designated I and II) were identified in the macrophage-like cell line P388D1. Lysophospholipase I was purified (8,500-fold) to homogeneity by DEAE-Sephacel, Sephadex G-75, Blue-Sepharose, and chromatofocusing chromatography. Lysophospholipase II was separated from the lysophospholipase I in the Blue-Sepharose step. The apparent molecular mass of lysophospholipase I and II are 27,000 and 28,000 daltons, respectively, determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Their pI values were 4.4 and 6.1 respectively, as determined by isoelectric focusing. Lysophospholipase I exhibited a broad pH optimum between 7.5-9.0. The double-reciprocal plot of the substrate dependence curve of the purified lysophospholipase I showed a break around the critical micelle concentration of the substrate (1-palmitoyl-sn-glycerol-3-phosphorylcholine). The apparent Km, determined from substrate concentrations above 10 microM was 22 microM, and the apparent Vmax was 1.3 mumol min-1mg-1. The purified enzyme did not have phospholipase A1, phospholipase A2, acyltransferase, or lysophospholipase-transacylase activity. No activity was detected toward triacylglycerol, diacylglycerol, p-nitrophenol acetate, p-nitrophenol palmitate, or cholesterol ester. The enzyme did, however, hydrolyze monoacylglycerol although at a rate 20-fold less than lysophospholipid, 0.06 mumol min-1mg-1. The lysophospholipase I was inhibited by fatty acids but not by glycerol-3-phosphorylcholine, glycerol-3-phosphorylethanolamine, or glyc-fjerol-3-phosphorylserine. A synthetic manoalide analogue 3(cis,cis,-7,10)hexadecadienyl-4-hydroxy-2-butenolide inhibited the enzyme with half-inhibition (IC50) at about 160 microM. Triton X-100 decreased the enzymatic activity, although this apparent inhibition can be explained by a "surface dilution" effect. The pure lysophospholipase I was stable for at least 5 months at -20 degrees C in the presence of glycerol and beta-mercaptoethanol. Lysophospholipid also demonstrated a protective effect during the later stage of purification.