Purification and characterization of the anticoagulant principle of Trimeresurus mucrosquamatus venom

Structure–function relationships and mechanism of anticoagulant phospholipase A2 enzymes from snake venoms

Phospholipase A(2) (PLA(2)) enzymes from snake venom are toxic and induce a wide spectrum of pharmacological effects, despite similarity in primary, secondary and tertiary structures and common catalytic properties. Thus, the structure-function relationships and the mechanism of this group of small proteins are subtle, complex and intriguing challenges. This review, taking the PLA(2) enzymes from spitting cobra (Naja nigricollis) venom as examples, describes the mechanism of anticoagulant effects. The strongly anticoagulant CM-IV inhibits both the extrinsic tenase and prothrombinase complexes, whereas the weakly anticoagulant PLA(2) enzymes (CM-I and CM-II) inhibit only the extrinsic tenase complex. CM-IV binds to factor Xa and interferes in its interaction with factor Va and the formation of prothrombinase complex. In contrast, CM-I and CM-II do not affect the formation of prothrombinase complex. In addition, CM-IV inhibits the extrinsic tenase complex by a combination of enzymatic and nonenzymatic mechanisms, while CM-I and CM-II inhibit by only enzymatic mechanism. These functional differences explain the disparity in the anticoagulant potency of N. nigricollis PLA(2) enzymes. Similarly, human secretory enzyme binds to factor Xa and inhibits the prothrombinase complex. We predicted the anticoagulant region of PLA(2) enzymes using a systematic and direct comparison of amino acid sequences. This region between 54 and 77 residues is basic in the strongly anticoagulant PLA(2) enzymes and neutral or negatively charged in weakly and non-anticoagulant enzymes. The prediction is validated independently by us and others using both site directed mutagenesis and synthetic peptides. Thus, strongly anticoagulant CM-IV binds to factor Xa (its target protein) through the specific anticoagulant site on its surface. In contrast, weakly anticoagulant enzymes, which lack the anticoagulant region fail to bind specifically to the target protein, factor Xa in the coagulation cascade. Thus, these studies strongly support the target model which suggests that protein-protein interaction rather than protein-phospholipid interaction determines the pharmacological specificity of PLA(2) enzymes.

Basic residues of human group IIA phospholipase A2 are important for binding to factor Xa and prothrombinase inhibition comparison with other mammalian secreted phospholipases A2

Human secreted group IIA phospholipase A2 (hGIIA) was reported to inhibit prothrombinase activity because of binding to factor Xa. This study further shows that hGIIA and its catalytically inactive H48Q mutant prolong the lag time of thrombin generation in human platelet-rich plasma with similar efficiency, indicating that hGIIA exerts an anticoagulant effect independently of phospholipid hydrolysis under ex vivo conditions. Charge reversal of basic residues on the interfacial binding surface (IBS) of hGIIA leads to decreased ability to inhibit prothrombinase activity, which correlates with a reduced affinity for factor Xa, as determined by surface plasmon resonance. Mutation of other surface-exposed basic residues, hydrophobic residues on the IBS, and His48, does not affect the ability of hGIIA to inhibit prothrombinase activity and bind to factor Xa. Other basic, but not neutral or acidic, mammalian secreted phospholipases A2 (sPLA2s) exert a phospholipid-independent inhibitory effect on prothrombinase activity, suggesting that these basic sPLA2s also bind to factor Xa. In conclusion, this study demonstrates that the anticoagulant effect of hGIIA is independent of phospholipid hydrolysis and is based on its interaction with factor Xa, leading to prothrombinase inhibition, even under ex vivo conditions. This study also shows that such an interaction involves basic residues located on the IBS of hGIIA, and suggests that other basic mammalian sPLA2s may also inhibit blood coagulation by a similar mechanism to that described for hGIIA.

Phospholipase A(2) with platelet aggregation inhibitor activity from Austrelaps superbus venom: protein purification and cDNA cloning

Four phospholipase A(2) (PLA(2)) enzymes (Superbins a, b, c, and d) with varying platelet aggregation inhibitor activities have been purified from Austrelaps superbus by a combination of gel filtration, ion-exchange, and reversed-phase high-pressure liquid chromatography. Purity and homogeneity of the superbins have been confirmed by high-performance capillary zone electrophoresis and mass spectrometry. The electron spray ionization mass spectrometry data showed that their molecular masses range from 13,140 to 13,236 Da. Each of the proteins has been found to be basic and exhibit varying degrees of PLA(2) activity. They also displayed different platelet aggregation inhibitory activities. Superbin a was found to possess the most potent inhibitory activity with an IC(50) of 9.0 nM, whereas Superbin d was found to be least effective with an IC(50) of 3.0 microM. Superbins b and c were moderately effective with IC(50) values of 0.05 and 0.5 microM, respectively. The amino-terminal sequencing confirmed the identity of these superbins. cDNA cloning resulted in the identification of 17 more PLA(2) isoforms in A. superbus venom. It has also provided complete information on the precursor PLA(2). The precursor PLA(2) contained a 27-amino-acid signal peptide and 117- to 125-amino-acid PLA(2) (molecular mass ranging from 13,000 to 14,000 Da). Two of these PLA(2) enzymes resembled more closely (87%) Superbin a in structure. Two unique PLA(2) enzymes containing an extra pancreatic loop also have been identified among the isoforms.

Inhibition of prothrombinase by human secretory phospholipase A2 involves binding to factor Xa

Human group II secretory phospholipase A2 (hsPLA2) exhibits significant anticoagulant activity that does not require its enzymatic activity. We examined which coagulation factor was targeted by hsPLA2 and analyzed which region of the protein may be involved in this inhibition. Prothrombin time coagulation assays indicated that hsPLA2 did not inhibit activated factor V (FVa) activity, whereas activated factor X (FXa) one-stage coagulation assays suggested that FXa was inhibited. The inhibitory effect of hsPLA2 on prothrombinase activity of FXa, FV, phospholipids, and Ca2+ complex was markedly enhanced upon preincubation of hsPLA2 with FXa but not with FV. Prothrombinase activity was also strongly inhibited by hsPLA2 in the absence of PL. High concentrations of FVa in the prothrombinase generation assay reversed the inhibitory effect of hsPLA2. By using isothermal titration calorimetry, we demonstrated that hsPLA2 binds to FXa in solution with a 1:1 stoichiometry and a Kd of 230 nM. By using surface plasmon resonance we determined the rate constants, kon and koff, of the FXa/hsPLA2 interaction and analyzed the Ca2+ effect on these constants. When preincubated with FXa, synthetic peptides comprising residues 51-74 and 51-62 of hsPLA2 inhibited prothrombinase assays, providing evidence that this part of the molecule, which shares similarities with a region of FVa that binds to FXa, is likely involved in the anticoagulant interaction of hsPLA2 with FXa. In conclusion, we propose that residues 51-62 of hsPLA2 bind to FXa at a FVa-binding site and that hsPLA2 decreases the prothrombinase generation by preventing FXa.FVa complex formation.

Purification and preliminary characterisation of praelongin phospholipases, antiplatelet agents from the snake venom of Acanthophis praelongus

Three praelongin phospholipases were chromatographically purified from the snake venom of Acanthophis praelongus. The purity and homogeneity of the praelongins were assessed by RP-HPLC, HPCE and mass spectrometry. The purified enzymes, praelongins 2bIII, 2cII and 2cIV were found to have phospholipase A2 activities with specific activities of 31.4 +/- 0.4, 326.1 +/- 10.2 and 362.5 +/- 12.0 U/mg, respectively. Mass spectrometry studies showed the molecular mass of praelongin 2bIII to be 12,782.9 +/- 2.6 and praelongins 2cII and 2cIV to have very similar molecular mass values, 12,971.4 +/- 4.5 and 12,971.9 +/- 3.6, respectively. However, platelet aggregation studies showed the praelongins to display different IC50 values, 180 microM for praelongin 2cII and 55 microM for praelongin 2cIV; praelongin 2bIII was found to be a more potent antiplatelet agent, having an IC50 of 0.65 microM. Praelongins 2bIII, 2cIV and 2cII were found to have pI values of 10.3 +/- 0.3, 9.6 +/- 0.6 and 9.4 +/- 0.6 as determined by HPCE. The antiplatelet potencies do not correspond to their in vitro phospholipase catalytic potencies, but appear to be related to the enzyme isoelectric points.

The anticoagulant effect of the human secretory phospholipase A2 on blood plasma and on a cell-free system is due to a phospholipid-independent mechanism of action involving the inhibition of factor Va

Blood platelets play a central role in haemostasis by leading to plug formation and by increasing the efficiency of blood coagulation. We have previously shown that blood platelets contain a group II secretory phospholipase A2 (sPLA2 grII) which is released into the extracellular medium upon activation but is unable to stimulate blood platelets. We presently reported an investigation of the putative involvement of the human sPLA2 grII (hsPLA2 grII) in the coagulation process, both in the absence and in the presence of activated platelets. We show that this enzyme prolongs the recalcification time of blood plasma even in the presence of activated platelets. The positive action of blood platelets on coagulation is correlated, at least in part, with the appearance at the cellular surface of procoagulant phospholipids which constitute a potential target for hsPLA2 grII. We therefore investigated the involvement of its enzymatic activity in the anticoagulant effect of this enzyme. We observed that the replacement of CaCl2 by SrCl2 to initiate the coagulation cascade did not suppress, but rather increased, the inhibitory action of hsPLA2 grII. Moreover, hsPLA2 grII hydrolyzed only a minor proportion of platelet phospholipids, and it did not affect plasma phospholipids. Taken together, these observations strongly suggest that the major action of hsPLA2 grII on blood coagulation does not involve the hydrolysis of phospholipids, in contrast with the strong anticoagulant effect of the group II venom phospholipase A2 from Crotalus durrissus terrificus. We next studied which step of the coagulation cascade was affected by hsPLA2 grII. Using purified coagulation factors, we demonstrated that hsPLA2 grII strongly inhibited the prothrombinase activity. This inhibitory effect was independent of the presence of phospholipids but required factor Va, leading to the hypothesis that hsPLA2 grII inhibited this factor. Further, the anticoagulant effect of hsPLA2 grII was observed on normal and factor-X-deficient plasma, but not on factor-V-deficient plasma. In conclusion, the anticoagulant action of hsPLA2 grII is based on a nonenzymatic mechanism of action involving the inhibition of factor Va.

Characterization of snake venom components acting on blood coagulation and platelet function

Snake venoms can affect blood coagulation and platelet function in various ways. The physicochemical properties and the mechanisms of actions of the snake venom components affecting blood coagulation and platelet function are discussed.

Effects of snake venom proteins on blood platelets

Snake venoms are complex mixtures which contain pharmacologically active polypeptides and proteins. Several snake venom constituents interfere in platelet aggregation, an important cellular process in thrombosis and hemostasis. These components range in size from small molecular weight polypeptides to high molecular weight proteins. Some of the proteins are enzymes, such as phospholipase A2, proteinases, nucleotidases, or L-amino acid oxidase, while others do not exhibit enzymatic activity. These components may initiate and/or inhibit platelet aggregation. Some venom factors induce platelet agglutination. This review deals with the physical characteristics of these venom factors, the mechanisms of their platelet effects, structure-function relationships, and their physiological significance.

A model to explain the pharmacological effects of snake venom phospholipases A2

Snake venom phospholipase A2 enzymes induce a wide variety of pathological symptoms in animals, despite sharing a common catalytic activity and similar structural features with nontoxic mammalian pancreatic enzymes. A hypothetical model is described to explain how specific pharmacological effects, such as presynaptic neurotoxicity, cardiotoxicity, myotoxicity, anticoagulant and platelet effects are exhibited by venom PLA2 enzymes. The model is an effort to elucidate many controversial and contradictory observations which have previously been difficult to interpret. The essential feature of the model is the targeting of venom PLA2 enzymes to the specific tissue or cell due to their affinity towards specific proteins, rather than lipid domains. After the initial binding, PLA2 enzymes induce various pharmacological effects by mechanisms which are either dependent or independent of their enzymatic activity. The model and its predicted target proteins thus provide a new focus for toxin research.

Edema formation and degranulation of mast cells by a basic phospholipase A2 purified from Trimeresurus mucrosquamatus snake venom

The basic phospholipase A2 (PLA2) purified from Trimeresurus mucrosquamatus snake venom was injected into the subplantar in order to induce edema formation in the rat hind paw. The maximum edema induced by PLA2 was induced at 1-2 hr after injection, and the per cent swelling curve showed a dose-dependent increase by PLA2 injection (2.5-10.0 micrograms). The rate of edema formation is different from the acute swelling induced by T. mucrosquamatus venom (TMV). Pretreatment with dexamethasone (4 mg/kg, s.c.), indomethacin (10 mg/kg, per 05) and diphenhydramine (100 mg/kg s.c.) inhibited the edema induced by the purified phospholipase A2. The injection of purified PLA2 or venom into rabbit skin resulted in an increase in vascular permeability which could be decreased by pretreatment with three antiinflammatory drugs. However, the pharmacological effect of dexamethasone (4 mg/kg) demonstrated a more effective inhibition than the other drugs in the PLA2-induced edema and vascular permeability change. Injection (i.p.) of PLA2 caused marked degranulation of mast cells in the rat mesentery which was facilitated by addition of calcium ion (10 mM) but antagonized by pretreating with three antiinflammatory agents. After incubating peritoneal mast cells with PLA2 (1.0 micrograms/ml), the release of histamine from the mast cell was approximately 36%, this effect was inhibited by preincubating the mast cell with three antiinflammatory agents.

Isolation and characterization of the major phospholipase A2 from the venom of Trimeresurus purpureomaculatus (shore pit viper)

1. The major phospholipase A2 (PLA-DE4) of the venom of Trimeresurus purpureomaculatus (shore pit viper) has been purified to electrophoretic homogeneity. 2. The isoelectric point of the purified enzyme was determined to be 4.20, and the mol. wt was 31,700 as estimated by Sephadex G-75 gel filtration chromatography; and 14,000 as estimated by SDS-polyacrylamide gel electrophoresis. The purified enzyme hydrolyzed phosphatidylcholine (PC) faster than phosphatidylethanolamine (PE), whereas phosphatidylserine (PS) was not hydrolyzed at all (PC greater than PE greater than PS =0). However, in reaction system consisted of mixtures of PC and PS, phosphatidylserine was effectively hydrolyzed by the enzyme. 4. The phospholipase A2 exhibited edema-forming activity but not hemolytic, hemorrhagic or anticoagulant activities. It was not lethal to mice at a dosage of 10 micrograms/g by i.v. route.

Effects of venom proteases on peptide chromogenic substrates and bovine prothrombin

Eighteen proteases were isolated from six hemorrhagic venoms of snakes belonging to the families of Crotalidae and Viperidae. According to their actions, they are classified as thrombin-like enzymes, alpha-fibrinogenases, beta-fibrinogenases, Factor X activator, prothrombin activator, hemorrhagins and esterases. Thrombin-like enzymes, beta-fibrinogenases, hemorrhagins and esterase hydrolyzed Phe-Pip-Arg-pNA (S-2238, substrate for thrombin) more strongly than CBZ-Ile-Glu-Gly-Arg-pNA (S-2222, substrate for Factor Xa), CBZ-Phe-Val-Arg-pNA (B-7632) or CBZ-Pro-Phe-Arg-pNA (B-2133). Thrombin-like enzymes, beta-fibrinogenase and esterase hydrolyzed tosyl-L-arginine methyl ester and benzoyl-L-arginine ethyl ester. S-2238 is the most susceptible chromogenic substrate for most venom proteases. Thrombin-like enzymes degraded prothrombin molecule progressively down to prethrombin 2 while alpha- and beta-fibrinogenases degraded it only to prethrombin 1. Factor X activator of Vipera russelli venom and esterase of T. mucrosquamatus venom did not have any effect on prothrombin. Thus, the effects of venom proteases on prothrombin are not parallel to their amidolytic or esterolytic effects.

Biological properties of Trimeresurus purpureomaculatus (shore pit viper) venom and its fractions

The toxic and biological activities of four samples of Trimeresurus purpureomaculatus venom were examined. The lethality, protein composition and biological activities of the four venom samples were similar. Three of the venom samples had LD50 (i.v.) values of 0.9 micrograms/g while the fourth had a lower LD50 (i.v.) of 0.45 micrograms/g. All four venom samples exhibited hemorrhagic, edema-inducing, anticoagulant and thrombin-like activities as well as the usual enzymes found in crotalid venoms. DEAE-Sephacel ion exchange chromatographic fractionation of the venom yielded 10 protein fractions. Only two fractions (fractions A and F) were lethal to mice; the major lethal fraction being fraction F. This fraction had an LD50 (i.v.) of 0.2 micrograms/g and exhibited hemorrhagic, edema-inducing and thrombin-like activity. It also exhibited phospholipase A, arginine ester hydrolase, arginine amidase, protease, 5'-nucleotidase, acetylcholinesterase and alkaline phosphomonoesterase activities. The lethal potency of fraction F is potentiated by fraction G, which exhibited anticoagulant activity as well as hemorrhagic, edema-inducing and enzymatic activities. Fractions F plus G account for almost 100% of the lethal potency of the venom.

Characterization of the anticoagulants from Taiwan cobra (Naja naja atra) snake venom

Taiwan cobra (Naja naja atra) snake venom was separated into 19 fractions by means of CM-Sephadex C-50 column chromatography. Anticoagulant Fractions V-VII were refractionated by gel filtration on Sephadex G-50 and the purified component possessed phospholipase A2 activity and an inhibitory effect on collagen-induced platelet aggregation. The anticoagulant action could be antagonized by phospholipid or platelet factor 3. Anticoagulant Fraction XVII was also further refractionated by gel filtration on Sephadex G-50 and the purified component was shown to be cardiotoxin. It was a weak anticoagulant, caused direct hemolysis and potentiated collagen-induced platelet aggregation. Thromboelastographic studies showed that the anticoagulant action of cobra venom is due to the synergistic effects of phospholipase A2 and cardiotoxin.

Mechanism of the anticoagulant, Cerastase F-4, isolated from Cerastes cerastes (Egyptian sand viper) venom

An anticoagulant enzyme, Cerastase F-4, from the venom of Cerastes cerastes was purified to homogeneity and was characterized (1). In the present report the mode of its fibrinogenolytic and fibrinolytic actions, and its effects on some other blood coagulation factors are described. Cerastes F-4 was shown to readily hydrolyze the alpha A chain of fibrinogen followed by the hydrolysis of the beta B chain. The gamma-chain was relatively resistant to hydrolysis. It also degrades the three chains of fibrin at different rates. The degradation products of the two substrates shown on SDS-polyacrylamide gel were quite different from those produced by plasmin, indicating different sites of cleavage by the enzyme. Using specific chromogenic substrates, Cerastase F-4 seems not to show thrombin-like, plasmin-like, kallikrein-like, antithrombin, or antiplasmin actions. Also, it does not activate prothrombin or plasminogen but degrades both of them slowly. It is concluded that the anticoagulation property of the purified enzyme, Cerastase F-4, is due to its destruction of fibrinogen.

Heat stable protein with anticoagulant and smooth muscle contractile actions isolated from Habu (Trimeresurus flavoviridis) venom

The biological activity of a Habu (Trimeresurus flavoiridis) venom fraction with drug-metabolizing enzyme inhibitory action was studied. The venom fraction, which was isolated through Sephadex G-100 gel filtration and cation exchange chromatography on Amberlite CG50, caused an increase of vascular permeability and hemorrhage, but these actions were lost after heating at 70 degrees C for 5 min. The fraction showed anticoagulant activity on citrated blood, and this activity remained after heating of the venom. Guinea pig ileum was contracted by treatment with nonheated or heated venom fraction, and these contractions were inhibited with atropine and potentiated with physostigmine. These results suggest that the drug-metabolizing enzyme inhibitor isolated from Habu venom involves the heat stable component with anticoagulant activity and smooth muscle contractile action.

Biphasic effect on platelet aggregation by phospholipase a purified from Vipera russellii snake venom

A basic phospholipase A was isolated from Vipera russellii snake venom. It induced a biphasic effect on washed rabbit platelets suspended in Tyrode's solution. The first phase was a reversible aggregation which was dependent on stirring and extracellular calcium. The second phase was an inhibitory effect on platelet aggregation, occurring 5 min after the addition of the venom phospholipase A without stirring or after a recovery from the reversible aggregation. The aggregating phase could be inhibited by indomethacin, tetracaine, papaverine, creatine phosphate/creatine phosphokinase, mepacrine, verapamil, sodium nitroprusside, prostaglandin E1 or bovine serum albumin. The venom phospholipase A released free fatty acids from synthetic phosphatidylcholine and intact platelets. p-Bromophenacyl bromide-modified venom phospholipase A lost its phospholipase A enzymatic and platelet-aggregating activities, but protected platelets from the aggregation induced by the native enzyme. The second phase of the venom phospholipase A action showed a different degree of inhibition on platelet aggregation induced by some activators in following order: arachidonic acid greater than collagen greater than thrombin greater than ionophore A23187. The longer the incubation time or the higher the concentration of the venom phospholipase A, the more pronounced was the inhibitory effect. The venom phospholipase A did not affect the thrombin-induced release reaction which was caused by intracellular Ca2+ mobilization in the presence of EDTA, but inhibited collagen-induced release reaction which was caused by Ca2+ influx from extracellular medium. The inhibitory effect of the venom phospholipase A and also lysophosphatidylcholine or arachidonic acid could be antagonized or reversed by bovine serum albumin. It was concluded that the first stimulatory phase of the venom phospholipase A action might be due to arachidonate liberation from platelet membrane. The second phase of inhibition of platelet aggregation and the release of ATP might be due to the inhibitory action of the split products produced by this venom phospholipase A.

Purification and properties of the main coagulant and anticoagulant principles of Vipera russellii snake venom

Vipera russellii venom was separated into thirteen fractions by means of DEAE-Sephadex A-50 column chromatography. Fraction III possessed anticoagulant and phospholipase A activities and Fraction XI possessed procoagulant and caseinolytic activities, both were further purified by gel filtration on Sephacryl S-200 column. Purified procoagulant (Component II) was a two-chain protein with molecular weight of 86 000 consisting of A-chain (Mr 66 000) and B-chain (Mr 20 000). It was a glycoprotein containing 7.8% neutral sugar and 715 amino-acid residues. The procoagulant activity was 10-times that of the crude venom. It was an acidic proteinase with isoelectric point of pH 4.2. Upon heat treatment at 60 degrees C, Component II was stable at pH 5.5 and 7.2 for 3 h, but was destroyed completely after 30 min at pH 8.9. It was devoid of esterase or amidase activity. Purified anticoagulant (Component I) was a single peptide chain with molecular weight of 16 000. It was carbohydrate free and contained 136 amino-acid residues. It was a basic protein with an isoelectric point of larger than pH 10. It was a potent phospholipase A with an enzymatic activity of 510 +/- 30 mumol/min per mg using phosphatidylcholine as substrate, and 1 microgram/ml was sufficient to cause 100% hemolysis by the indirect hemolytic method. Upon heat treatment at 90 degrees C, Component I was heat stable at pH 5.5 for more than 3 h, but was destroyed completely after 2 h at pH 7.2 and 8.9. The anticoagulant activity of Component I could be neutralized by platelet factor 3, tissue thromboplastin and cephalin.

Effect of the purified phospholipases A2 from snake and bee venoms on rabbit platelet function

Effects of seven purified phospholipases A2 from the venoms of snakes (Naja naja atra, Trimeresurus mucrosquamatus and T. gramineus) and honey bee (Apis mellifera) on rabbit washed platelet suspension in the absence of bovine serum albumin have been studied. Only phospholipases A2 from N. n. atra, T. mucrosquamatus and A. mellifera venoms induced platelet aggregation with small amounts of 14C-serotonin release. They showed tachyphylaxis and also cross-tachyphylaxis in inducing platelet aggregation. The former two phospholipases A2 exhibited biphasic responses in which irreversible aggregations appeared at concentrations of 1-10 micrograms/ml. At higher concentrations, they elicited the reversible aggregation. Exogenous Ca2+ was essential to their activity. Indomethacin and EDTA completely abolished both phospholipase A2 induced platelet shape change and aggregation, while mepacrine, prostaglandin E1, verapamil and nitroprusside inhibited only the aggregation response. p-Bromophenacyl bromide-modified phospholipases A2, which almost completely lost enzymatic activity, failed to induce platelet aggregation. Phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol inhibited the phospholipase A2-induced platelet aggregation. These phospholipases A2 induced thromboxane B2 formation which was inhibited by EDTA and indomethacin, but not by prostaglandin E1. Pre-treatment of platelet suspension with phospholipase A2 from N. n. atra or A. mellifera venom (50 micrograms/ml) inhibited platelet aggregation induced by sodium arachidonate or collagen, but not that induced by thrombin or ionophore A-23187. Exogenous sodium arachidonate or lysophosphatidylcholine also showed unaltered inhibitory spectrum on platelet aggregation. It is concluded that phospholipases A2 induce platelet aggregation by virtue of their enzymatic activity, cleaving the membrane phospholipids resulting in arachidonic acid release and formation of thromboxane A2. On the other hand, the cleaved products, lysophosphatidylcholine, arachidonic acid or arachidonate metabolites (via lipoxygenase pathway) may be responsible for anti-platelet activity.

Presynaptic and musculotropic effects of a basic phospholipase A2 from the Formosan habu (Trimeresurus mucrosquamatus) venom

A basic phospholipase A2 purified from the venom of a crotalid snake (Trimeresurus mucrosquamatus) was applied to chick and mouse neuromuscular preparations. The enzyme at lower concentrations (1-3 micrograms/ml) blocks neuromuscular transmission at a presynaptic site, while at higher concentrations (10-30 micrograms/ml) it causes contracture and depolarization of the muscle as well. It is concluded that the mode of action of the enzyme on vertebrate nerve-muscle transmission is similar to that of notexin and ceruleotoxin from elapid snake venoms.

Edema formation and degranulation of mast cells by Trimeresurus mucrosquamatus snake venom

Trimeresurus mucrosquamatus venom, carrageenin, compound 48/80, trypsin and bovine serum albumin were injected s.c. into the plantar muscle to induce edema formation in the hind paw of rats. The venom was the most potent, and it and compound 48/80 induced the maximum swelling rate of edema within 15 - 30 min after injection. The edema volume induced by the venom was dose-dependent between 2.5 and 10 micrograms. Hydrocortisone, phenylbutazone, indomethacin and diphenhydramine inhibited edema induced by the venom and other inflammatory agents. Diphenhydramine was the most effective inhibitor of edema and increased vascular permeability induced by the venom. Injection of the venom i.p. caused exocytosis and degranulation of mesentery mast cells with a decreased electron density of released granules. Systemic administration of diphenhydramine inhibited the venom-induced exocytosis. Diphenhydramine and pyrilamine inhibited the contraction of guinea-pig ileum caused by venom or compound 48/80. It is concluded that histamine released from mast cells plays an important role in the causation of the edema induced by Trimeresurus mucrosquamatus snakebites.

Cardiotoxin from Naja naja atra snake venom: a potentiator of platelet aggregation

Cardiotoxin, isolated from Naja naja atra snake venom, potentiates platelet aggregation induced by ADP, thrombin, collagen and venom phospholipase A2. The malondialdehyde formation caused by ADP, thrombin and venom phospholipase A2 were also increased in the presence of cardiotoxin. Both potentiation of aggregation and increase in malondialdehyde were blocked by indomethacin or Ca2+ (5 mM or 0.05 mM). Cardiotoxin did not potentiate thrombin-induced aggregation of p-bromophenacyl bromide-modified platelets. Thromboxane B2 formation induced by thrombin or collagen was also increased by cardiotoxin, while that by arachidonate was not affected. As a membrane-active polypeptide, cardiotoxin might augment the Ca2+-flux during the activation of the platelet membrane by aggregation inducers and then increase the activation of endogenous phospholipase A2.

Characterization of a fibrinogenase from northern copperhead (Agkistrodon contortrix mokasen) venom

One of the fractions obtained by the carboxymethylcellulose ion-exchange chromatography of northern copperhead (Agkistrodon contortrix mokasen) venom prevented the thrombin-induced clotting of fibrinogen by proteolytically degrading the fibrinogen. The active component has been further purified to apparent electrophoretic homogeneity by molecular sieve chromatography. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis indicated a molecular weight of 22 900 +/- 600 for the purified enzyme. In addition to its fibrinogenase activity, it catalyzed the hydrolysis of hide power azure and had an intraperitoneal LD50 value in mice of less than 5.1 microgram/g body weight. The enzyme rapidly destroyed fibrinogen's ability to form clots. Electrophoresis of fibrinogen which had been incubated only a few minutes with the fibrinogenase revealed the rapid disappearance of the alpha-chain and the appearance of lower molecular weight fragments. The neutral pH optimum and ethylenediamine-tetraacetic acid (EDTA) and dithiothreitol sensitivity indicated that this enzyme belonged to the class metalloproteinases. Atomic absorption studies have revealed one zinc atom per molecule of protein. The apoenzyme's activity was restored by incubation with ZnCl2.

A potent platelet aggregation inducer purified from Trimeresurus mucrosquamatus snake venom

A non-coagulant platelet aggregation inducer (called platelet 'aggregoserpentin') was isolated from Trimeresurus mucrosquamatus snake venom by CM-Sephadex chromatography and purified by gel filtration. It was homogeneous as judged by the ultracentrifugal analysis and electrophoresis on polyacrylamide gel and cellulose acetate membrane. The molecular weight was estimated to be 68 000 as judged by the SDS-polyacrylamide gel electrophoresis and gel filtration on Sephadex G-75. The ultracentrifugal analysis gave 3.19 Svedberg units. It was a protein-polysaccharide complex containing 340 amino acid residues and 50% carbohydrate per molecule. The isoelectric point was pH 5.4. It did not possess any of the hydrolase enzymatic properties which were found in the crude venom. The minimal concentration of 'aggregoserpentin' necessary to induce platelet aggregation was 10 ng/ml, about one four-hundredth of that of the crude venom. It did not cause lysis of platelets because lactate dehydrogenase was not found in supernatant after complete aggregation. An intravenous injection of 'aggregoserpentin' (35 microgram/kg) into rabbit ear marginal vein caused marked decrease of platelet number to approx. 10-20% of that of the control.