Purification and characterization of canine myocardial cytosolic phospholipase A2. A calcium-independent phospholipase with absolute f1-2 regiospecificity for diradyl glycerophospholipids

Recently, we identified a novel calcium-independent, plasmalogen-selective phospholipase A2 activity in canine myocardial cytosol which represents the major measurable phospholipase A2 activity in myocardial homogenates (Wolf, R. A., and Gross, R. W. (1985) J. Biol. Chem. 260, 7295-7303). We now report the 154,000-fold purification of this phospholipase A2 to homogeneity through utilization of sequential anion exchange, chromatofocusing, affinity, Mono Q, and hydroxylapatite chromatographies. The purified enzyme had a molecular mass of 40 kDa, possessed a specific activity of 227 mumol/mg min, had a pH optimum of 6.4, and catalyzed the regiospecific cleavage of the sn-2 fatty acid from diradyl glycerophospholipids. The purified polypeptide was remarkable for its ability to selectively hydrolyze plasmenylcholine in homogeneous vesicles (subclass rank order: plasmenylcholine greater than alkyl-ether choline glycerophospholipid greater than phosphatidylcholine) as well as in mixed bilayers comprised of equimolar plasmenylcholine/phosphatidylcholine. Purified myocardial phospholipase A2 also possessed selectivity for hydrolysis of phospholipids containing arachidonic acid at the sn-2 position in comparison to oleic or palmitic acid. Taken together, these results constitute the first purification of a calcium-independent phospholipase with absolute regiospecificity for cleavage of the sn-2 acyl linkage in diradyl glycerophospholipids and demonstrate that myocardial phospholipase A2 has kinetic characteristics which are anticipated to result in the selective hydrolysis of sarcolemmal phospholipids during myocardial ischemia.     

Purification,characterization and biological activities of phospholipase a from russell's viper (Vipera russelli) venom

• 1.1. The major phospholipase A has been purified to electrophoretic homogeneity from the venom of Vipera russelli (Russell's viper).
• 2.2. The molecular weight of the purified enzyme was estimated to be 31,000 by Sephadex G-75 gel filtration chromatography and 29,000 by SDS-polyacrylamide gel electrophoresis. The enzyme exhibited an apparent K_m value of 2.3 × 10⁻² M.
• 3.3. The phospholipase A showed edema forming, indirect hemolytic and myonecrotic activities but not hemorrhagic activity.

     

Purification, characterization and bactericidal activities of basic phospholipase A2 from the venom of Agkistrodon halys (Chinese pallas)

Agkistrodon snake venoms contain a variety of phospholipases (PLA(2)), some of which are myotoxic. In this study, we used reverse-phase HPLC to purify PLA(2) from the venom of Agkistrodon halys. The enzyme named as AgkTx-II, a basic Asp49 PLA(2), has a molecular masses of 13,869.05. The amino acid sequence and molecular mass of AgkTx-II was identical to those of an Asp49 basic myotoxic PLA(2) previously isolated from this venom. Antibacterial activities were tested by susceptibility and broth-dilution assays. AgkTx-II exerted a potent antibacterial activity against Staphylococcus aureus, Proteus vulgaris, Proteus mirabilis, and Burkholderia pseudomallei. The MIC values of AgkTx-II ranged between 85 and 2.76muM and was most effective against S. aureus, P. vulgaris, P. mirabilis (MIC of 21.25muM) and B. pseudomallei (MIC of 10.25muM). This AgkTx-II rapidly killed S. aureus, P. vulgaris and B. pseudomallei in a dose-dependent manner. The effect of the AgkTx-II on bacterial membranes was evaluated by scanning and transmission electron microscopy. AgkTx-II caused morphological alterations apparent on their cellular surfaces, suggesting a killing mechanism based on membrane permeabilization and damage. Cytotoxicity was measured by XTT tetrazolium (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide) and lactate dehydrogenase (LDH) assays using U-937 cells (monocytes). The AgkTx-II did not affect cell viability up to 500muM concentrations but cell death was evident at 1000muM concentration after 24 and 48h. Furthermore, the repeated exposure of AgkTx-II (2-14muM) treated mice showed different tissue alterations, mainly at the brain and kidney; the toxicological potential of AgkTx-II remains to be elucidated. The AgkTx-II exhibits no hemolytic action even at high doses (10-100muM) in human erythrocytes. However, the AgkTx-II is believed to exert its bactericidal effect by permeabilizing the bacterial membrane by forming pores. In addition, the basic PLA(2) AgkTx-II displays a bactericidal effect, which may be either dependent or independent of catalysis.     

1-Cys peroxiredoxin, a bifunctional enzyme with glutathione peroxidase and phospholipase A2 activities

This report provides definitive evidence that the protein 1-Cys peroxiredoxin is a bifunctional ("moonlighting") enzyme with two distinct active sites. We have previously shown that human, rat, and bovine lungs contain an acidic Ca(2+)-independent phospholipase A(2) (aiPLA(2)). The cDNA encoding aiPLA(2) was found to be identical to that of a non-selenium glutathione peroxidase (NSGPx). Protein expressed using a previously reported E. coli construct which has a His-tag and 50 additional amino acids at the NH(2) terminus, did not exhibit aiPLA(2) activity. A new construct which contains the His-tag plus two extra amino acids at the COOH terminus when expressed in Escherichia coli generated a protein that hydrolyzed the sn-2 acyl chain of phospholipids at pH 4, and exhibited NSGPx activity with H(2)O(2) at pH 8. The expressed 1-Cys peroxiredoxin has identical functional properties to the native lung enzyme: aiPLA(2) activity is inhibited by the serine protease inhibitor, diethyl p-nitrophenyl phosphate, by the tetrahedral mimic 1-hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol (MJ33), and by 1-Cys peroxiredoxin monoclonal antibody (mAb) 8H11 but these agents have no effect on NSGPx activity; NSGPx activity is inhibited by mercaptosuccinate and by 1-Cys peroxiredoxin mAb 8B3 antibody which have no effect on aiPLA(2) activity. Mutation of Ser(32) to Ala abolishes aiPLA(2) activity, yet the NSGPx activity remains unaffected; a Cys(47) to Ser mutant is devoid of peroxidase activity but aiPLA(2) activity remains intact. These results suggest that Ser(32) in the GDSWG consensus sequence provides the catalytic nucleophile for the hydrolase activity of aiPLA(2), while Cys(47) in the PVCTTE consensus sequence is at the active site for peroxidase activity. The bifunctional catalytic properties of 1-Cys peroxiredoxin are compatible with a simultaneous role for the protein in the regulation of phospholipid turnover as well as in protection against oxidative injury.     

Phosphatidic acid phosphatase and phospholipase A activities in plasma membranes from fusing muscle cells

Plasma membranes from fusing embryonic muscle cells were assayed for phospholipase A activity to determine if this enzyme plays a role in cell fusion. The membranes were assayed under a variety of conditions with phosphatidylcholine as the substrate and no phospholipase A activity was found. The plasma membranes did contain a phosphatidic acid phosphatase which was optimally active in the presence of Triton X-100 and glycerol. The enzyme activity was constant from pH 5.2 to 7.0, and did not require divalent cations. Over 97% of the phosphatidic acid phosphatase activity was in the particulate fraction. The subcellular distribution of the phosphatidic acid phosphatase was the same as the distibutions of the plasma membrane markers, $\text{Na}{}^{\mathrm{+}}\text{+ K}{}^{\mathrm{+}}$)-ATPase and the acetylcholine receptor, which indicates that this phosphatase is located exclusively in the plasma membranes. There was no detectable difference in the phosphatidic acid phosphatase activities of plasma membranes from fusing and non-fusing cells.     

Purification and properties of debranching enzyme from dogfish muscle.

Glycogen debranching enzyme (4-alpha-glucanotransferase amylo-1,6-glucosidase, EC 2.4.1.25 + 3.2.1.33) was purified 140-fold from dogfish muscle in a rapid, high-yield procedure that takes advantage of a strong binding of the enzyme to glycogen, and its quantitative adsorption to concanavalin A-Sepharose only when the polysaccharide is present. The final product was hrophoresis in the presence and absence of dodecyl sulfate. A molecular weight of 162,000 +/- 5000 was determined by sedimentation equilibrium analysis in good agreement with the value of 160,000 estimated by gel electrophoresis, but a low-sedimentation constant of 6.5 S suggests that the enzyme is asymmetric. The molecule appears to be made up of a single polypeptide chain with no evidence for multiple repeating sequences: it could not be dissociated into smaller fragments by dodecyl sulfate even after complete carboxymethylation; tryptic cleavage of the native protein yielded only two fragments of molecular weight 20,000 and 140,000 without loss of enzymatic activity. The amino acid composition of the enzyme is reported; no covalently bound phosphate or carbohydrate could be detected. All 32 sulfhydryl groups present were titrated with 5,5'-dithiobis(2-nitrobenzoic acid) under denaturing conditions; eight reacted readily in the native enzyme without loss of catalytic activity, while substitution of eight additional ones lowered the activity by 50%. Inactivation was greatly reduced by glycogen; the polysaccharide also influenced markedly the electrophoretic behavior of the enzyme and large filamentous aggregates were formed when solutions of both were mixed. Purified debranching enzyme releases 3 mumol of glucose min-1 mg-1 at 19 degrees C, pH 6.0, from a glycogen limit dextrin and one-tenth this amount when the native polysaccharide is used as substrate; glycogen is quantitatively degraded in the presence of phosphorylase. None of the usual sugar phosphates or nucleotide effectors of glycolysis affected enzymatic activity. No phosphorylation by either dogfish or rabbit skeletal muscle protein kinase or phosphorylase kinase could be demonstrated, nor any direct interaction with phosphorylase as measured by SH-group reactivity, enzymatic activity, or rate of phosphorylase b to a conversion. Purification of the 160,000 molecular weight M-line protein of skeletal muscle resulted in the quantitative removal of debranching enzyme, indicating that the two proteins are different.     

Monosodium urate crystals stimulate phospholipase A2 enzyme activities and the synthesis of a phospholipase A2-activating protein

Eicosanoids are important mediators of the inflammatory response to monosodium urate crystals (MSUC) that results in gout. Phospholipase enzymes cleave fatty acids from membrane phospholipids, and this is thought to be the rate-limiting step in eicosanoid production. To understand better the mechanism of eicosanoid production in this disease, we stimulated human peripheral blood neutrophils and monocytes with MSUC and measured phospholipase enzyme activities. MSUC stimulated both intracellular and secretory phospholipase A2 enzyme activities in a time and concentration-dependent manner. Specificity was observed, as phospholipase C activities were not affected. Pretreatment with colchicine, but not aspirin, indomethacin, allopurinol, or islet activating protein, abrogated the enhanced phospholipase A2 activities. We have recently isolated and characterized a phospholipase A2 activating protein termed PLAP from synovial fluid from patients with rheumatoid arthritis, and from murine and bovine cell lines. PLAP was detected in gouty synovial fluid by immunodot blotting and ELISA assays and expressed the same characteristics as PLAP identified from other sources. To examine the role of PLAP in MSUC-induced phospholipase A2 stimulation, we treated cells with MSUC and observed an increase in immunoreactive PLAP. This response also could be blunted by colchicine, but not other drugs. Both phospholipase A2 and PLAP induced production by human monocytes of PGE2 and leukotriene B4 by neutrophils. These findings suggest that phospholipase A2 activation in response to MSUC requires an intact microtubule structure, and that phospholipase A2 and PLAP may be important modulators of at least a portion of the gouty inflammatory response.     

Purification and properties of cytosolic malic enzyme from human skeletal muscle

1. An NADP+-dependent malic enzyme was purified 7940-fold from the cytosolic fraction of human skeletal muscle with a final yield of 55.8% and a specific activity of 38.91 units/mg of protein. 2. The purification to homogeneity was achieved by ammonium sulfate fractionation, DEAE-Sepharose chromatography, affinity chromatography on NADP+-Agarose, gel filtration on Sephacryl S-300 and rechromatography on the affinity column. 3. Either Mn2+ or Mg2+ was required for activity: the pH optima with Mn2+ and Mg2+ were 8.1 and 7.5, respectively. The enzyme showed Michaelis-Menten kinetics. At pH 7.5 the apparent Km values with Mn2+ and Mg2+ for L-malate and NADP+ were 0.246 mM and 5.8 microM, and 0.304 mM and 5.8 microM, respectively. The Km values with Mn2+ for pyruvate, NADPH and bicarbonate were 8.6 mM, 6.1 microM and 22.2 mM, respectively. 4. The enzyme was also able to decarboxylate malate in the presence of NAD+. At pH 7.5 the reaction rate was approximately 10% of the rate in the presence of NADP+, with a Km value for NAD+ of 13.9 mM. 5. The following physical parameters were established: s0(20.w) = 10.48, Stokes' radius = 5.61 nm, pI = 5.72 Mr of the dissociated enzyme = 61,800. The estimates of the native apparent Mr yielded a value of 313,000 upon gel filtration, and 255,400 with f/fo = 1.33 by combining the chromatographic data with the sedimentation measurements. 6. The electron microscopy analysis of the uranyl acetate-stained enzyme revealed a tetrameric structure. 7. Investigations to detect sugar moieties indicated that the enzyme contains carbohydrate side chains, a property not previously reported for any other malic enzyme.     

Purification and properties of phospholipase A2 from the venom of scorpion, (Heterometrus fulvipes)

Phospholipase A2 was purified about 78 fold from the venom of scorpion Heterometrus fulvipes. The molecular weight of the enzyme was found to be 16,000 and it was optimally active at pH 7.4 and at 50 degrees C. The Km value of the enzyme was 1.8 x 10(-3) M. Calcium, Magnesium and Zinc ions stimulated whereas Mercury ion and EDTA inhibited the enzyme activity. This enzyme exhibited fluorescence emission maximum between 310-320 nm.     

Purification of a Class B1 platelet aggregation inhibitor phospholipase A2 from Indian cobra (Naja Naja) venom

A platelet aggregation inhibitor phospholipase A(2) (NND-IV-PLA(2)) was isolated from Naja naja (Eastern India) venom by a combination of cation and anion exchange chromatography. NND-IV-PLA(2) is the most catalytically active enzyme isolated from the Indian cobra venom. The acidic PLA(2) profile of Eastern regional Indian cobra venom is distinctly different from that of the western regional venom. However the acidic PLA(2)s from both the regions follow the pattern of increasing catalytic activity with increase in acidic nature of the PLA(2) isoform. NND-IV-PLA(2) is a Class B1 platelet aggregation inhibitor and inhibits platelet aggregation induced by ADP, collagen and epinephrine. Modification of active site histidine abolishes both catalytic activity and platelet aggregation inhibition activities while aristolochic acid, a phospholipase A(2) inhibitor has only partial effect on the two activities.     

Purification, characterization, and cDNA sequencing of cytosolic phospholipase A(2) from equine neutrophils

It has been demonstrated that equine neutrophils, but not eosinophils, require exogenous arachidonic acid for calcium ionophore A23187-induced leukotriene synthesis. Because cytosolic phospholipase A(2) (cPLA(2)) plays an essential role in leukotriene formation in leukocytes, we investigated the presence of a functional cPLA(2) in equine neutrophils. To determine whether cPLA(2) from neutrophils was catalytically active, we purified the enzyme >6,500 fold with 3% recovery from equine neutrophils. The full-length cDNA sequence encoded a 749-amino acid protein. The deduced amino acid sequence demonstrated 95% identity with human and mouse cPLA(2), as well as 83 and 73% identity with chicken and zebra fish cPLA(2) protein, respectively. The equine cPLA(2) possessed some properties that distinguished the equine enzyme from the human enzyme. First, the enzyme activity of the equine cPLA(2) was differently influenced by cations as compared with the human cPLA(2). Second, the equine neutrophil cPLA(2) migrated as an approximately 105-kDa protein, in comparison with human cPLA(2) which migrated as a 110-kDa protein. A difference between equine neutrophils and eosinophils in the degree of phosphorylation of the cPLA(2) protein was observed. Thus, the cPLA(2) protein from eosinophils was constitutively phosphorylated, while the cPLA(2) protein from neutrophils was unphosphorylated.In summary, these results demonstrate that equine neutrophils indeed express an active cPLA(2) protein but that there is a difference in the degree of phosphorylation of the cPLA(2) protein between equine neutrophils and eosinophils. This difference might explain the difference between the two cell types in the capacity to produce leukotrienes from endogenous substrate.     

Purification and characterization of a novel phospholipase A2 from king cobra (Ophiophagus hannah) venom

A novel phospholipase A₂, designated as Oh-DE-2, was isolated from the venom ofOphiophagus hannah (king cobra) by successive chromatography on SP-Sephadex C-25, DE-52, and Q-Sepharose columns. Oh-DE-2 with pI 5.1 showed an apparent molecular weight of 14 kD as revealed by SDS-PAGE and gel filtration. The amino acid sequence was homologous with those of PLA₂s from Elapidae venoms. Oh-DE-2 was effectively inactivated byp-bromophenacyl bromide, indicating that the conserved His-48 is essential for its enzymatic activity. However, modification of the conserved Trp-19 did not cause a precipitous drop in the enzymatic activity of Oh-DE-2 as observed with PLA₂s fromNaja naja atra andBungarus multicinctus venoms. A quenching study showed that the microenvironment of Trp in Oh-DE-2 was inaccessible to acrylamide, iodide, or cesium, a finding which was different from those observed with PLA₂s fromN. naja atra andB. multicinctus venoms. These results might suggest that, unlike other PLA₂ enzymes, Trp-19 in Oh-DE-2 is not directly involved in its enzymatic mechanisms.     

Purification of two lipases with high phospholipase A1 activity from guinea-pig pancreas

• 1.1. Two cationic lipases (Ia and Ib) were purified from homogenates of fresh guinea-pig pancreas by ion-exchange chromatography on DEAE-Sepharose and CM-Sepharose (twice for the latter) followed by gel filtration on Sephadex G-100.
• 2.2. Both enzymes were homogeneous upon polyacrylamide gel electrophoresis. Their molecular weights are 37000 and 42000 for lipases Ia and Ib, respectively, as determined by gel filtration on Sephadex G-100. Very close values for isoelectric points were found in the pH range 9.3–9.4.
• 3.3. The cationic lipases are characterized by a high phospholipase A activity (500 IU/mg protein using a potentiometric assay with egg yolk lecithin as substrate), resulting in an unusual phospholipase/lipase activity ratio of 1.
• 4.4. Using doubly labelled phosphatidylcholine, a specificity, A₁, was described for the two enzymes, which are unaffected by N-ethylmaleimide, diisopropylfluorophosphate and p-bromophenacylbromide. The enzymes are insensitive to EDTA and slightly inhibited by CaCl₂and MgCl₂, whereas sodium deoxycholate is required for maximal activity.

     

Purification and characterization of angiotensin-converting enzyme (ACE) from sheep lung

Molecular Biology Reports - Angiotensin-converting enzyme (ACE, EC 3.4.15.1) in the renin-angiotensin system regulates blood pressure by catalyzing angiotensin I to the vasoconstrictor angiotensin...     

Purification and characterization of phospholipase A2 from rat stomach

Phospholipase A2, which is localized in the mucosal part of the corpus of rat stomach (Hirohara et al. (1987) Biochim. Biophys. Acta 919, 231-238), was purified 990-fold from the supernatant of a tissue homogenate by heat treatment at acidic pH, ammonium sulfate fractionation, ion-exchange chromatography, gel-filtration and reverse-phase high-performance liquid chromatography (reverse-phase HPLC). The purified enzyme gave a single protein band on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis with a molecular mass of approx. 17 kDa. The enzyme had a pH optimum of 8.0 and hydrolyzed the 2-arachidonoyl residue of phosphatidylcholine preferentially to the 2-oleoyl residue, the Vmax and Km values for the two being 227 and 29 mumol/min per mg protein and 0.037 and 0.019 mM, respectively. The activity was calcium-dependent and was markedly increased by SDS and dimethyl sulfoxide (DMSO). The enzyme showed typical product inhibition. Free unsaturated fatty acids (oleic, arachidonic and docosahexaenoic acids), which are supposedly the main enzymatic products in vivo, inhibited the activity. Arachidonic acid caused noncompetitive inhibition and its concentration for its maximal inhibition (50% inhibition) was 5 x 10(-5) M. Lysophosphatidylcholine, free saturated fatty acids (palmitic and stearic acids) and arachidonic acid metabolites (leukotrienes and prostaglandins) had no effect on the activity.