Isolation and characterization of toxic proteins from the venom of the Brazilian scorpion Tityus serrulatus

Novel components of Tityus serrulatus venom: A transcriptomic approach

Several research groups have studied the components produced by the venom gland of the scorpion Tityus serrulatus, which has one of the most lethal venoms in the world. Various methodologies have been employed to clarify the complex mechanisms of action of these components, especially neurotoxins and enzymes. Transcriptomes and proteomes have provided important information for pharmacological, biochemical, and immunological research. Next-generation sequencing (NGS) has allowed the description of new transcripts and completion of partial sequence descriptions for peptides, especially those with low expression levels. In the present work, after NGS sequencing, we searched for new putative venom components. We present a total of nine new transcripts with neurotoxic potential (Ts33-41) and describe the sequences of one hyaluronidase (TsHyal_4); three enzymes involved in amidation (peptidyl-glycine alpha-amidating monooxygenase A, peptidyl-alpha-hydroxyglycine alpha-amidating lyase, and peptidylglycine alpha-hydroxylating monooxygenase), which increases the lethal potential of neurotoxins; and also the enzyme Ts_Chitinase1, which may be involved in the venom's digestive action. In addition, we determined the level of transcription of five groups: toxins, metalloproteases, hyaluronidases, chitinases and amidation enzymes, including new components found in this study. Toxins are the predominant group with an expression level of 91.945%, followed by metalloproteases with only 7.790% and other groups representing 0.265%.

Ts1 from the Brazilian scorpion Tityus serrulatus: A half-century of studies on a multifunctional beta like-toxin

The Tityus serrulatus scorpion species represents a serious human health threat to in Brazil because it is among the animals that produces the most dangerous venoms for mammals in South America. Its venom has provided several highly selective ligands that specifically interact with sodium and potassium channels. During the past decades, several international groups published an increasing amount of data on the isolation and the chemical, pharmacological and immunological characterisation of its main β-toxin, Ts1. In this review, we compiled the best available past and recent knowledge on Ts1. Aside from its intricate purification, the state-of-the-art understanding concerning its pharmacological activities is presented. Its solved three-dimensional structure is shown, as well as the possible surface areas of contact between Ts1 and its diverse voltage-gated Na⁺ channel targets. Organisations of the gene and the precursor encoding Ts1 are also tackled based on available cDNA clones or on information obtained from polymerase chain reactions of stretches of scorpion DNA. At last, the immunological studies complete with Ts1 to set up an efficient immunotherapy against the Tityus serrulatus venom are summarized.

Effects of Brazilian scorpion venoms on the central nervous system

In Brazil, the scorpion species responsible for most severe incidents belong to the Tityus genus and, among this group, T. serrulatus, T. bahiensis, T. stigmurus and T. obscurus are the most dangerous ones. Other species such as T. metuendus, T. silvestres, T. brazilae, T. confluens, T. costatus, T. fasciolatus and T. neglectus are also found in the country, but the incidence and severity of accidents caused by them are lower. The main effects caused by scorpion venoms - such as myocardial damage, cardiac arrhythmias, pulmonary edema and shock - are mainly due to the release of mediators from the autonomic nervous system. On the other hand, some evidence show the participation of the central nervous system and inflammatory response in the process. The participation of the central nervous system in envenoming has always been questioned. Some authors claim that the central effects would be a consequence of peripheral stimulation and would be the result, not the cause, of the envenoming process. Because, they say, at least in adult individuals, the venom would be unable to cross the blood-brain barrier. In contrast, there is some evidence showing the direct participation of the central nervous system in the envenoming process. This review summarizes the major findings on the effects of Brazilian scorpion venoms on the central nervous system, both clinically and experimentally. Most of the studies have been performed with T. serrulatus and T. bahiensis. Little information is available regarding the other Brazilian Tityus species.

Electrophysiological characterization of Ts6 and Ts7, K⁺ channel toxins isolated through an improved Tityus serrulatus venom purification procedure

In Brazil, Tityus serrulatus (Ts) is the species responsible for most of the scorpion related accidents. Among the Ts toxins, the neurotoxins with action on potassium channels (α-KTx) present high interest, due to their effect in the envenoming process and the ion channel specificity they display. The α-KTx toxins family is the most relevant because its toxins can be used as therapeutic tools for specific target cells. The improved isolation method provided toxins with high resolution, obtaining pure Ts6 and Ts7 in two chromatographic steps. The effects of Ts6 and Ts7 toxins were evaluated in 14 different types of potassium channels using the voltage-clamp technique with two-microelectrodes. Ts6 toxin shows high affinity for Kv1.2, Kv1.3 and Shaker IR, blocking these channels in low concentrations. Moreover, Ts6 blocks the Kv1.3 channel in picomolar concentrations with an IC₅₀ of 0.55 nM and therefore could be of valuable assistance to further designing immunosuppressive therapeutics. Ts7 toxin blocks multiple subtypes channels, showing low selectivity among the channels analyzed. This work also stands out in its attempt to elucidate the residues important for interacting with each channel and, in the near future, to model a desired drug.

Serrumab: a novel human single chain-fragment antibody with multiple scorpion toxin-neutralizing capacities

In Brazil, scorpion envenomation is an important public health problem. The yellow scorpion, Tityus serrulatus (Ts), is considered the most dangerous species in the country, being responsible for the most severe clinical cases of envenomation. Currently, the administration of serum produced in horses is recognized and used as a treatment for accidents with scorpions. However, horse herds' maintenance is costly and the antibodies are heterologous, which can cause anaphylaxis and Serum Sickness. In the present work, a human monoclonal fragment antibody, Serrumab, has been analysed. Toxin neutralizing effects of Serrumab were evaluated using a two-electrode voltage-clamp technique. The results show that Serrumab presented a high neutralizing effect against Ts β-toxins (Ts1, 43.2% and Ts2, 68.8%) and none or low neutralizing effect against α-toxins (Ts3, 0% and Ts5, 10%). Additional experiments demonstrated that Serrumab was also able to neutralize the action of toxins from other scorpion genus (Css II, 45.96% and Lqh III, 100%/β- and α-toxins, respectively). This work indicated that Serrumab is able to neutralize many toxins in Ts venom, and could being considered as a neutralizing antibody for formulating a human anti-scorpion serum in Brazil. Additionally, this work demonstrated that Serrumab could neutralize different toxins from distinct scorpion genus. All these results reinforce the idea that Serrumab is a scFv antibody with multiple neutralizing capacities and a promising candidate for inclusion in scorpion anti-venoms against different genera.

Investigation of the relationship between the structure and function of Ts2, a neurotoxin from Tityus serrulatus venom

Scorpion toxins targeting voltage-gated sodium (Na(V)) channels are peptides that comprise 60-76 amino acid residues cross-linked by four disulfide bridges. These toxins can be divided in two groups (α and β toxins), according to their binding properties and mode of action. The scorpion α-toxin Ts2, previously described as a β-toxin, was purified from the venom of Tityus serrulatus, the most dangerous Brazilian scorpion. In this study, seven mammalian Na(V) channel isoforms (rNa(V)1.2, rNa(V)1.3, rNa(V)1.4, hNa(V)1.5, mNa(V)1.6, rNa(V)1.7 and rNa(V)1.8) and one insect Na(V) channel isoform (DmNa(V)1) were used to investigate the subtype specificity and selectivity of Ts2. The electrophysiology assays showed that Ts2 inhibits rapid inactivation of Na(V)1.2, Na(V)1.3, Na(V)1.5, Na(V)1.6 and Na(V)1.7, but does not affect Na(V)1.4, Na(V)1.8 or DmNa(V)1. Interestingly, Ts2 significantly shifts the voltage dependence of activation of Na(V)1.3 channels. The 3D structure of this toxin was modeled based on the high sequence identity (72%) shared with Ts1, another T. serrulatus toxin. The overall fold of the Ts2 model consists of three β-strands and one α-helix, and is arranged in a triangular shape forming a cysteine-stabilized α-helix/β-sheet (CSαβ) motif.

Serrumab: a human monoclonal antibody that counters the biochemical and immunological effects of Tityus serrulatus venom

In Brazil, the species Tityus serrulatus is responsible for the most severe cases of scorpion envenomation. There is currently a need for new scorpion anti-venoms that are more effective and less harmful. This study attempted to produce human monoclonal antibodies capable of inhibiting the activity of T. serrulatus venom (TsV), using the Griffin.1 library of human single-chain fragment-variable (scFv) phage antibodies. Four rounds of phage antibody selection were performed, and the round with the highest phage antibody titer was chosen for the production of monoclonal phage antibodies and for further analysis. The scFv 2A, designated serrumab, was selected for the production and purification of soluble antibody fragments. In a murine peritoneal macrophage cell line (J774.1), in vitro assays of the cytokines interleukin (IL)-6, tumor necrosis factor (TNF)-α, and IL-10 were performed. In male BALB/c mice, in vivo assays of plasma urea, creatinine, aspartate transaminase, and glucose were performed, as well as of neutrophil recruitment and leukocyte counts. It was found that serrumab inhibited the TsV-induced increases in the production of IL-6, TNFα, and IL-10 in J774.1 cells. The in vivo inhibition assay showed that serrumab also prevented TsV-induced increases in the plasma levels of urea, creatinine, aspartate transaminase, and glucose, as well as preventing the TsV-induced increase in neutrophil recruitment. The results indicate that the human monoclonal antibody serrumab is a candidate for inclusion in a mixture of specific antibodies to the various toxins present in TsV. Therefore, serrumab shows promise for use in the production of new anti-venom.

Intrahippocampal injection of TsTX-I, a beta-scorpion toxin, causes alterations in electroencephalographic recording and behavior in rats

AIMS

TsTX-I scorpion toxin, also known as γ-toxin, is a β-toxin which binds to site 4 of the sodium channel, shifting its activation potential. There are few studies about its pharmacological action in the central nervous system. The objective of this work was to determine the electroencephalographic, behavioral and histopathological effects of intrahippocampal injection of TsTX-I.

MAIN METHODS

Rats were anesthetized and fitted with cannulae for injection into the hippocampus and with electrodes for cerebral recording. The animals were treated with Ringer solution, some doses of TsTX-I, DMSO 0.1% or veratridine. Behavioral and electrographic recordings were observed for 4 hours after the injection. After 7 days, the rats were perfused, and their brains removed for histological analysis.

KEY FINDINGS

Increasing doses of the toxin evoked epileptic-like discharges, wet dog shakes, and in some cases hind limb paralysis and intense respiratory difficulty followed by death. The histopathological analysis demonstrated no cell loss. Animals injected with veratridine developed epileptiform activity in the electrographic recording and neuronal loss.

SIGNIFICANCE

The results suggest that TsTX-I toxin may be responsible, at least in part, for the epileptic and behavioral effects observed with the crude venom, and although veratridine and TsTX-I act on Na-channel, the differences between them are remarkable, demonstrating that toxins can have different functional effects depending on the site of action in the channel. Thus, animal neurotoxins are often highly selective and may be useful for the identification of the sequence of events underlying neurotransmission.

Scorpion venom and the inflammatory response

Scorpion venoms consist of a complex of several toxins that exhibit a wide range of biological properties and actions, as well as chemical compositions, toxicity, and pharmacokinetic and pharmacodynamic characteristics. These venoms are associated with high morbility and mortality, especially among children. Victims of envenoming by a scorpion suffer a variety of pathologies, involving mainly both sympathetic and parasympathetic stimulation as well as central manifestations such as irritability, hyperthermia, vomiting, profuse salivation, tremor, and convulsion. The clinical signs and symptoms observed in humans and experimental animals are related with an excessive systemic host inflammatory response to stings and stings, respectively. Although the pathophysiology of envenomation is complex and not yet fully understood, venom and immune responses are known to trigger the release of inflammatory mediators that are largely mediated by cytokines. In models of severe systemic inflammation produced by injection of high doses of venom or venoms products, the increase in production of proinflammatory cytokines significantly contributes to immunological imbalance, multiple organ dysfunction and death. The cytokines initiate a cascade of events that lead to illness behaviors such as fever, anorexia, and also physiological events in the host such as activation of vasodilatation, hypotension, and increased of vessel permeability.

Effects of voltage-gated Na+ channel toxins from Tityus serrulatus venom on rat arterial blood pressure and plasma catecholamines

Scorpion toxins interact with ionic channels of excitable cells, leading to a massive release of neurotransmitters. Voltage-gated Na+ channel toxins are mainly responsible for the toxic effects of scorpion envenoming and can be classified into two classes: alpha- and beta-neurotoxins. TsTX-V and TsTX-I from Tityus serrulatus venom (TsV) are, respectively, examples of these toxins. In this work, we compared the effects of these toxins on mean arterial pressure (MAP) and catecholamines release in rats. Toxins were isolated by ion exchange chromatography (TsTX-I) followed by RP-HPLC (TsTX-V). All experiments were performed on conscious unrestrained rats previously catheterised. The toxins (15 and 30 microg/kg) and TsV (50 and 100 microg/kg) were injected intravenously. MAP was continuously monitored through femoral catheter. Epinephrine (E) and norepinephrine (NE) levels were determined by RP-HPLC with electrochemical detection, at 10 min before and 2.5, 30 and 90 min after treatments. Maximal pressor effects were observed at 2.5-3.5 min. TsV induced intense long lasting increase in MAP, as did TsTX-I. TsTX-V showed the lowest pressor effects. TsV showed the highest effects on catecholamines release, followed by TsTX-I and TsTX-V with maximal effect at 2.5 min, followed by a gradual reduction, however remaining higher than controls. Although both toxins act on Na+ channels, TsTX-I displayed significant and more intense effects on catecholamines release and blood pressure than TsTX-V. It seems that the toxicity of TsTX-V is not related only with its ability to release catecholamines, indicating that other neurotransmitters, may be involved in its toxicity.

Epitope mapping of the antigenic protein TsNTxP from Tityus serrulatus scorpion venom using mouse, rabbit and sheep antibodies

In the present investigation we used native and recombinant TsNTxP to elicit antibodies in three different animal models (mouse, rabbit and sheep). Differences among anti-TsNTxP antibodies were analyzed using sets of overlapping pentadecapeptides of the TsNTxP amino acid sequence and also modified peptides to reveal key residues in antibody-peptide binding. Despite the identification of similar peptides by the antibodies in the C and N-terminal, peculiarities of each system were observed including the level of reactivity and also the number and type of key residues in the continuous epitopes of TsNTxP. In addition, in vitro neutralization assays indicated that sheep are an alternative and efficient model for the production of anti-Tityus serrulatus venom.

Dopamine release evoked by beta scorpion toxin, tityus gamma, in prefrontal cortical slices is mediated by intracellular calcium stores

1. We have investigated the effect of tityus gamma (TiTX gamma) scorpion toxin on the release of [3H]dopamine in rat brain prefrontal cortical slices. The stimulatory effect of TiTX gamma on the release of [3H]dopamine was dose/time-dependent with an EC50 of 0.01 microM. 2. Tetrodotoxin blocked the TiTX gamma-induced release of [3H]dopamine, indicating the dependency for Na+ channels. 3. EGTA had no effect on the TiTX gamma-induced release of [3H]dopamine, indicating the process is independent of extracellular calcium. Release of [3H]dopamine evoked by TiTX gamma was inhibited by 57% by BAPTA, a chelator of intracellular calcium. 4. Xestospongin and 2-APB, putative blockers of IP3-sensitive release of intracellular calcium stores, caused an equal and significant inhibition of 24% of the TiTX gamma-induced release of [3H]dopamine, while the slight inhibition evoked by dantrolene, a putative blocker of ryanodine-sensitive calcium store was not significant. 5. Nomifensine and ascorbic acid, blockers of dopamine transporter (DAT), caused an inhibition of 27 and 29%, respectively, on the toxin-induced release of [3H]dopamine suggesting that most of the TiTX gamma-induced release of dopamine is not due to the reversal of Na+ gradient. 6. In conclusion the majority of the TiTX gamma-induced release of [3H]dopamine is exocytotic and mobilizes calcium from the intracellular IP3-sensitive calcium stores.

Most cited papers in Toxicon

Citation of a published work is one of the parameters considered in the analysis of relevance and importance of scientific contributions. In 2002, for the first time the Impact Factor of Toxicon has risen above 2.0, placing it at the 17th position among 76 journals in the 'toxicology' field. The aim of this article was to identify the most cited articles in Toxicon, that have contributed to the steady increase of its Impact Factor. The number of citations, complete reference and type of all documents appearing in Toxicon in the period 1963-2003 were retrieved from the ISI Web-of-Science homepage. The documents retrieved were sorted by the number of citations received. A 'citation index', defined as the number of citations divided by the number of years since publication, was calculated for each document. It was clearly seen that reviews in Toxicon received 4.4-fold more citations than articles. Unexpectedly, it was found that recent papers were proportionally more cited than old ones. A decrease in the proportion of papers dealing on 'snake*' through out the period and the broadened range of subjects of the most cited papers recently published in Toxicon reflects an increased 'visibility' in other fields of toxinology. Research on plant toxins gained its own space in Toxicon with newer publications showing high citation indexes. It can be postulated that these facts helped to increase Toxicon's Impact Factor from 1.248 in 1999 to 2.003 in 2002. With the increased number of issues in Toxicon as well as publications of subject-dedicated volumes containing mostly reviews, the Impact Factor of Toxicon is expected to keep rising in the near future.

Lung compliance, plasma electrolyte levels and acid-base balance are affected by scorpion envenomation in anesthetized rats under mechanical ventilation

To determine the effects of Tityus serrulatus scorpion toxin on lung compliance and resistance, ionic equilibrium and acid-base balance over time in anesthetized and mechanically ventilated rats, we measured air flow, tracheal and esophageal pressure. Lung volume was obtained by electronic integration of airflow signal. Arterial blood samples were collected through a catheter at baseline (before) and 5, 15, 30 and 60 min after scorpion toxin injection for arterial blood gases, bicarbonate, and alkali reserve levels as well as for, sodium, potassium, magnesium, glucose, lactate, hematocrit, and osmolality analysis. Injection of the gamma fraction of the T. serrulatus scorpion venom in rats under mechanical ventilatory support leads to a continuous decrease in lung compliance secondary to pulmonary edema, but no change in airway resistance. The changes in arterial blood gases characterizing metabolic acidosis were accompanied by an increase in arterial lactate and glucose values, suggesting a scorpion toxin-induced lactic acidosis, in association with poor tissue perfusion (hypotension and low cardiac output). Moreover, scorpion toxin injection resulted in hyperosmolality, hyperkalemia, hypermagnesemia and an increase in hematocrit. The experiments have shown a clinically relevant animal model to study severe scorpion envenoming and may help to better understand the scorpion envenoming syndrome.

Age effects on the pharmacokinetics of tityustoxin from Tityus serrulatus scorpion venom in rats

The pharmacokinetics of scorpion venom and its toxins has been investigated in experimental models using adult animals, although, severe scorpion accidents are associated more frequently with children. We compared the effect of age on the pharmacokinetics of tityustoxin, one of the most active principles of Tityus serrulatus venom, in young male/female rats (21-22 days old, N=5-8) and in adult male rats (150-160 days old, N=5-8). Tityustoxin (6 microg) labeled with 99mTechnetium was administered subcutaneously to young and adult rats. The plasma concentration vs time data were subjected to non-compartmental pharmacokinetic analysis to obtain estimates of various pharmacokinetic parameters such as total body clearance (CL/F), distribution volume (Vd/F), area under the curve (AUC), and mean residence time. The data were analyzed with and without considering body weight. The data without correction for body weight showed a higher Cmax (62.30 +/- 7.07 vs 12.71 +/- 2.11 ng/ml, P<0.05) and AUC (296.49 +/- 21.09 vs 55.96 +/- 5.41 ng h(-1) ml(-1), P<0.05) and lower Tmax (0.64 +/- 0.19 vs 2.44 +/- 0.49 h, P<0.05) in young rats. Furthermore, Vd/F (0.15 vs 0.42 l/kg) and CL/F (0.02 +/- 0.001 vs 0.11 +/- 0.01 l h(-1) kg(-1), P<0.05) were lower in young rats. However, when the data were reanalyzed taking body weight into consideration, the Cmax (40.43 +/- 3.25 vs 78.21 +/- 11.23 ng kg(-1) ml(-1), P<0.05) and AUC (182.27 +/- 11.74 vs 344.62 +/- 32.11 ng h(-1) ml(-1), P<0.05) were lower in young rats. The clearance (0.03 +/- 0.002 vs 0.02 +/- 0.002 l h(-1) kg(-1), P<0.05) and Vd/F (0.210 vs 0.067 l/kg) were higher in young rats. The raw data (not adjusted for body weight) strongly suggest that age plays a pivotal role in the disposition of tityustoxin. Furthermore, our results also indicate that the differences in the severity of symptoms observed in children and adults after scorpion envenomation can be explained in part by differences in the pharmacokinetics of the toxin.

Alkylation of myotoxic phospholipases A2 in Bothrops moojeni venom: a promising approach to an enhanced antivenom production

Bothrops moojeni crude venom (MjCV) and its two major toxins, namely myotoxin I (MjTX-I) and myotoxin II (MjTX-II) were alkylated by p-bromophenacyl bromide (BPB). After alkylation the i.p. LD(50) (mice) of MjCV and MjTX-I/II increased from 6.0 to 15.7mg/kg and from 8.0 to 45.0mg/kg, respectively. In addition, doses of 5x LD(50) of alkylated MjTX-I did not cause a single death in mice and no myonecrosis was detected for the alkylated toxins, although both proteins still induced edema. Antibodies to native and modified crude venom or myotoxins cross-reacted with 12 purified class II myotoxic phospholipases A(2) found in snake venoms of the genus Bothrops. Myotoxic PLA(2)s from class I and class III were not recognized by the above antibodies. These results suggest that the overall antigenic structure is conserved among class II myotoxic PLA(2)s, despite differences in their amino acid sequences. Anti-MjTX-I-BPB and anti-MjTX-II-BPB rabbit serum, obtained against the modified myotoxins, were apparently more efficient than those obtained against the native myotoxins. In neutralization experiments, pre-incubation of crude venom or isolated myotoxins with antibodies raised against the native or modified toxins inhibited their PLA(2) and myotoxic activities. Therefore, alkylation of His48 by BPB strongly reduces the local tissue damage induced by B. moojeni venom or isolated myotoxins while retaining antigenicity, which suggests a promising procedure for an enhanced antiophidian serum production for practical purposes.

Effects of alpha-scorpion toxin, tityustoxin on the release of [3H] dopamine of rat brain prefrontal cortical slices

The effect of tityustoxin (TsTX) on the release of [3H] dopamine in rat brain prefrontal cortical slices was investigated. The stimulatory effect of TsTX was dependent on incubation time and TsTX concentration with an EC50 of 0.05 microM. The release of [3H] dopamine stimulated by TsTX is dependent of Na+ channels and thus, was completely, inhibited by tetrodotoxin. Tityustoxin-induced release of [3H] dopamine was not blocked by ethylene glycol-bis(beta-aminoethyl) ether (EGTA) and thus was independent of extracellular calcium. However, [3H] dopamine release induced by TsTX was inhibited by 52% by BAPTA, a calcium chelator. Moreover, dantrolene (100 microM) and tetracaine (500 microM) partially inhibited by 38 and 29%, respectively, the tityustoxin-induced release of [3H] dopamine from prefrontal cortical slices suggesting a role from intracellular calcium increase. In conclusion, part of the TsTX-induced release [3H] dopamine may be due to an effect of the toxin on the reversal of the dopamine transporter (DAT), but the majority of the toxin stimulated release of [3H] dopamine involves the mobilization of intracellular calcium stores.

PnTx4-3, a new insect toxin from Phoneutria nigriventer venom elicits the glutamate uptake inhibition exhibited by PhTx4 toxic fraction

Several pools of neurotoxic peptides obtained from fractionated Phoneutria nigriventer venom induce different toxicological effects. One of them, PhTx4, is highly toxic towards insects and displays only a slight toxicity when injected in mice. Also, this fraction contains a class of peptides that are able to inhibit glutamate uptake in preparations of mammalian central nervous systems (CNS). In this work a new toxin called PnTx4-3 was isolated from the PhTx4 fraction by reverse phase and anion exchange steps using high performance liquid chromatography (HPLC). Edman sequencing of PnTx4-3 revealed that it was a polypeptide of 48 amino acid residues, containing 10 cysteines cross-linked by five disulfide bridges. The molecular mass measured by ES-Q-TOF mass spectrometry was 5199.49+/-0.64 Da, which is very close to the calculated mass from amino acid sequence (5199.99 Da). This toxin induces immediate excitatory effects when injected intrathoracically in house flies and cockroaches. Intracerebroventricular injections of 30 microg of PnTx4-3 in mice resulted in no apparent signs of intoxication. In order to make an orthologous comparison, pharmacological characterisation were carried out in rat brain synaptosomes by using [3H]-L-glutamate, showed that the whole PhTx4 fraction as well as the pure toxins PnTx4-3, Tx4(6-1) and Tx4(5-5) obtained of this fraction, were able to inhibit the glutamate uptake in the micromolar concentration range. PnTx4-3 inhibits the glutamate uptake in a dose dependent manner, with an IC50 of approximately 1 microM. PnTx4-3 is highly homologous to the Tx4(6-1) and Tx4(5-5) toxins previously described from the same fraction.

Effect of age on body distribution of Tityustoxin from Tityus serrulatus scorpion venom in rats

Previous research from our Laboratory has shown a greater susceptibility of young animals, when compared to adults, to envenomation by tityustoxin (TsTX), one of the main toxins from Tityus serrulatus scorpion venom. Our hypothesis is that a differential body distribution of TsTX among adult and young animals could account for the worse prognosis of scorpion envenomation in infants. Thus, TsTX labeled with technetium-99m was injected (6 microg, subcutaneous) in adult (150-160 day-old) and young (21-22 day-old) male rats. Groups of animals were sacrificed at different times after TsTX injection (0.08, 1.0, 3.0, 6.0, 12.0 and 24.0 hours) under Urethane anesthesia (140 mg/100 g, i.p.). The brain, heart, lungs, liver, kidneys, spleen and thyroid were excised and blood collected. Young rats presented a shorter latency toxin concentration peak in all studied organs except for the liver and the kidney, when compared to adults. The ratio between the area under the curve of the toxin concentration in each organ and that in blood (Kp) indicates higher accumulation in the organs of young animals mainly for brain, liver and heart. These observations suggest a faster toxin distribution in the organs of young rats. The higher uptake of TsTX in the brain is suggestive of a greater permeability for the toxin along the blood-brain barrier of young rats. In conclusion, the higher uptake in heart, together with data from the brain, may help to elucidate the clinical manifestations frequently observed in children under scorpion envenomation.

Centrally injected tityustoxin produces the systemic manifestations observed in severe scorpion poisoning

In this work we submitted adult male Wistar rats to intracerebroventricular (icv) and iv microinjections of the fraction tityostoxin (TsTX) from the Tityus serrulatus scorpion venom, to address whether the CNS could account for the systemic alterations previously reported: cardiac arrhythmias, lung edema, and seizures. Animals were injected icv, total volume of 1.0 microl, with either sterile saline (n = 4) or differing doses of TsTX (1.74, n = 5; 0.174, n = 4; 0.087, n = 5; and 0.058 microg, n = 4). The peripheral effect of the highest dose of TsTX used (1.74 microg) was tested through iv injections in the femoral vein (n = 4). All animals were recorded by a Video EEG/ECG system for a maximum period of 90 mins or until death. After recording, the lungs were harvested and weighed to evaluate edema (lung/body wt x100). Our results show that icv injections of TsTX, but not iv injections, were able to provoke heart arrhythmias, lung edema, and seizures. Furthermore, the toxin was capable of producing epileptiform discharges in all animals injected with 1.74 microg of the toxin. In conclusion, the action of TsTX in the CNS may solely account for the peripheral alterations observed in severe cases of Tityus serrulatus scorpion poisoning.

A microdialysis study of glutamate concentration in the hippocampus of rats after TsTX toxin injection and blockade of toxin effects by glutamate receptor antagonists

Scorpion toxins act on ionic channels changing the release of neurotransmitters. In the present study, we investigated the glutamatergic release evoked by intrahippocampal injection of TsTX toxin isolated from Tityus serrulatus scorpion venom in male Wistar rats and the blockade of the toxin effect by glutamatergic antagonists. Microdialysis for neurotransmitter level quantification, electroencephalographic recording, and histopathological analysis were performed. The microdialysis method revealed enhanced levels of extracellular glutamate in the hippocampal area. The toxin injection preceded by injection of the glutamate receptor antagonists dizolcipine maleate (MK-801), D(-)2-amino-5-phosphonopentanoic acid (AP-5), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), L(+)-2-amino-3-phosphonopropionic acid (AP-3), and (+)-alpha-methyl-4-carboxyphenylglycine (MCPG) demonstrated that MK-801 and AP-5 fully blocked the electrographic alterations and the CA1 cell loss induced by the toxin. CNQX, AP-3, and MCPG partially blocked the epileptiform discharges and no hippocampal damage was observed. Thus, we conclude that the toxin evokes glutamate release and that glutamate receptor antagonists can partially or totally block the toxin effect.

Modulation of Na+-channels by neurotoxins produces different effects on [3H]ACh release with mobilization of distinct Ca2+-channels

1. Voltage-gated Na+ channels are responsible for initiation and conduction of action potentials. The arrival of an action potential at nerve terminal increases intracellular Na+ and Ca2+ concentrations. Calcium entry into neurons through voltage-dependent calcium channels is associated with a variety of intracellular processes. Scorpion neurotoxins have been used as tools to investigate mechanisms involved in neurotransmitter release. Tityustoxin (TsTX) is an alpha-type toxin that delays Na+-channel inactivation. Toxin-gamma (TiTX-gamma) is a beta-type toxin that induces Na+-channel activation at resting potentials. 2. In the present work, we describe the effects of both toxins on [3H]acetylcholine ([3H]ACh) release from rat cerebrocortical synaptosomes, in the presence or absence of the calcium channels blockers: omega-conotoxin-GVIA (omega-CgTx), 1 microM; omega-agatoxin-IVA (omega-Aga), 30 nM; omega-conotoxin-MVIIC (omega-MVIIC), 1 microM; or verapamil, 1 microM. 3. TsTX evokes [3H]ACh release in a concentration-dependent manner with a gradual increase up to saturation at concentrations of 500 nM. However, release of ACh evoked by TiTX-gamma was not linear regarding the toxin concentration. The [3H]-ACh release evoked by TsTX or TiTX-gamma was partially inhibited by omega-CgTx or omega-Aga, and blocked with omega-MVIIC. Verapamil (1 microM) had no effect. Tetrodotoxin blocked [3H]ACh release evoked by both toxins. 4. These results show that different actions on Na+-channels produce different effects on [3H]ACh release with involvement of distinct presynaptic Ca2+-channels, which supports the idea that sodium channels may modulate neurotransmitter release.

Technetium-99m labeling of tityustoxin and venom from the scorpion Tityus serrulatus

The tityustoxin, the most toxic fraction from scorpion Tityus serrulatus venom, has been used as a tool in several neurochemical and neuropharmacological studies. Biological activities of labeled and unlabeled tityustoxin and venom were compared. The samples were labeled in the presence of stannous chloride and sodium borohydride with a yield of 60-70% for the venom and 75-85% for tityustoxin and then chromatographed in Sephadex G-10. Biological activities of tityustoxin and venom were preserved after labeling.

Phenobarbital blocks the lung edema induced by centrally injected tityustoxin in adult Wistar rats

The aim of this study was to evaluate the ability of phenobarbital to block the lung edema observed after intracerebroventricular (icv) injections of tityustoxin (TsTX), a toxic fraction of the Tityus serrulatus venom. We injected 1.74 microg icv (1.0 microl) of TsTX in Wistar rats pre-treated with 0.1 ml intramuscular injections of sterile saline or phenobarbital (60 or 170 mg/kg body weight). After the experiments the lungs were harvested and the pulmonary index (PI = lung/body weight x 100) calculated. The animals pre-treated with saline developed severe lung edema (PI = 1.8 +/- 0.2) after TsTX icv injection whereas those that received 170 mg/kg of phenobarbital presented no lung edema (PI = 0.71 +/- 0.02). Our results suggest that the lung edema induced by TsTX is of neurogenic nature and that 170 mg/kg of phenobarbital blocks TsTX induced lung edema.

Investigation of the modulation of glutamate release by sodium channels using neurotoxins

The modulation of neurotransmitter release by calcium channels is well established, yet, sodium channels were regarded mainly as charge carriers. Many lines of evidence suggest a more fine-tuning role played by sodium channels. Using rat cerebrocortical isolated nerve endings (synaptosomes) and two toxins that have separate sites of action on sodium channels and provoke distinct changes in channel kinetics, we were able to show that depending on the rate of increase in channel conductance, the outcome in terms of neurotransmitter release and calcium channel types coupled to that event are different. Mainly, our study focused on veratridine, an alkaloid from lilaceous plants that binds to sodium channel toxin site 2, and tityustoxin, a toxin purified from the venom of the Brazilian yellow scorpion Tityus serrulatus that binds to site 3. Veratridine induces a slower increase in intrasynaptosomal sodium and calcium concentrations, slower depolarization, delayed exocytosis and a slower and predominantly calcium-independent glutamate release, when compared to tityustoxin.Thus, we have used these two toxins to investigate the events that start with sodium entry and culminate with the release of glutamate in isolated nerve endings (synaptosomes) from rat cerebral cortex. With that in mind we measured intrasynaptosomal free sodium concentration [Na(+)](i), intrasynaptosomal free calcium concentration [Ca(2+)](i), membrane potential, exocytosis and glutamate release using fluorescent probes.

Release of gamma-[(3)H]aminobutyric acid in rat brain cortical slices by alpha-scorpion toxin

In this paper, the effect of the alpha-scorpion toxin tityustoxin (TsTX) in the release of gamma-[(3)H]aminobutyric acid ([(3)H]GABA) from rat brain cortical slices is described. The TsTX-stimulatory effect on the release of [(3)H]GABA was dependent on incubation time and TsTX concentration, having an EC(50) of 0.33 microM. Tetrodotoxin (TTX) completely inhibited the TsTX action on [(3)H]GABA release. The scorpion toxin effect was calcium-dependent and involves P/Q calcium channels. beta-Alanine also induces the release of [(3)H]GABA that was not inhibited by TTX but was additive in the presence of TsTX. The data suggest a neuronal origin for the release of [(3)H]GABA by TsTX.

Mechanisms underlying the structural alterations of the rat submandibular gland induced by Tityus serrulatus tityustoxin

As the mechanisms underlying the structural changes induced in rat submandibular glands by Tityus serrulatus tityustoxin have not been reported, the present study was undertaken to investigate the participation of adrenergic and muscarinic cholinergic receptors in these alterations. Most of the stimulatory effects of the toxin are observed in the secretory cells of the acini and granular convoluted tubules (GCT). We evaluated the ability of the toxin to induce morphological changes in acinar and GCT cells after adrenoreceptor and cholino receptor blockage. The influence of tityustoxin-induced adrenal discharge on the acinar and GCT cells was also investigated after bilateral adrenalectomy. We show that the intense cytoplasmic vacuolation of the acinar cells induced by tityustoxin was prevented by prazosin (alpha(1) adenoreceptor blockade) and atropine (muscarinic cholinoreceptor blockade). The decrease of GCT cell granules following tityustoxin injection was completely blocked by prasozin and partially by propranolol. These results indicate that acinar vacuolation, degranulation of GCT cells, reduction of GCT diameter and height of its epithelium depends on tityustoxin induced adrenergic and cholinergic mechanisms. In contrast, tityustoxin induced acinar cell degranulation was not modified by atropine, prasozin or propranolol (beta(1)-beta(2) adenoreceptor blockade). Thus, acinar degranulation seems to be due to a direct action of tityustoxin on of the rat submandibular glands. The degranulation of the GCT cells and the acinar vacuolation was also prevented by bilateral adrenalectomy, suggesting that these effects are mostly due to catecholamines released from the adrenal glands.

Tracking sodium channels in live cells: confocal imaging using fluorescently labeled toxins

One particularly important class of ion channels in excitable cells are the voltage-dependent sodium channels (VDSC). Knowledge of the distribution of VDSC in living cells is important for studies of neuronal excitability, development, and plasticity. Here, we demonstrate a new method for visualizing the spatial distribution of VDSC in living cells. To illustrate the capabilities of the technique, the distribution of VDSC in GH3 cells was revealed with fluorescent derivatives of the alpha-type and beta-type scorpion toxins in conjunction with laser scanning confocal microscopy. Cells exhibited fluorescent hot spots on the surface of the membrane. This characteristic staining pattern was prevented by pre-incubation with unlabeled native toxins and blocked by membrane depolarization for alpha-type toxins. Labeling was not observed in cells lacking sodium channels (HEK 293) after incubation with fluorescent-labeled toxins. Image processing techniques were applied to identify the location of each cluster of labeled VDSC in these cells. The proposed method eliminates artefacts commonly introduced during sample preparation for immunostaining and should prove to be a valuable research tool for investigating VDSC distribution in living specimens.

Beta-scorpion toxin induces the release of gamma-[3 H]aminobutyric acid in rat brain slices

The effect of the beta-scorpion toxin, TiTX gamma on the release of [3H]GABA from rat brain cortical slices is described. The stimulatory effect of TiTX gamma on the release of [3H]GABA was dependent on incubation time and TiTX gamma concentration with an EC50 of 0.19 microM. The scorpion toxin effect was calcium dependent and was completely inhibited by tetrodotoxin. beta-Alanine also induced the release of [3H]GABA and this effect was not inhibited by tetrodotoxin but was additive in the presence of TiTX gamma. The data suggest a neuronal origin for the release of [3H]GABA by TiTX gamma.

Spider neurotoxins block the beta scorpion toxin-induced calcium uptake in rat brain cortical synaptosomes

In this paper we describe the effects of the beta scorpion toxin Tityus gamma (TiTX gamma) and spider neurotoxins Tx3-3 and Tx3-4 in the (45)Ca(2+) uptake in synaptosomes. The TiTX gamma-stimulatory effect on (45)Ca(2+) uptake in synaptosomes was inhibited omega-Conotoxin MVIIC (omega-CgTX MVIIC) (0.1 microM) and omega-Agatoxin IVA (0.1 microM) by 70% and 41%, respectively. omega-CgTX MVIIC (1.0 microM) almost completely blocked the TiTX gamma-induced (45)Ca(2+) uptake in synaptosomes. Verapamil (1.0 microM) and omega-Conotoxin GVIA (0.1 microM) had no effect in the scorpion toxin-induced (45)Ca(2+) influx. The spider neurotoxins Tx3-3 and Tx3-4 inhibited the TiTX gamma-induced calcium uptake with an IC(50) of 10.0 and 30.0 nM, respectively. It is suggested that spider neurotoxins Tx3-3 and Tx3-4 blocking effect in the TiTX gamma-induced calcium uptake involves P/Q-type calcium channels.

Tityustoxin effect on nerve compound action potentials requires extracellular sodium

Previous studies have demonstrated that Li(+) ions can substitute for Na(+) in a variety of functional systems. Using the single sucrose-gap recording technique, we measured the nerve compound action potential to study the effects of tityustoxin (an alpha-scorpion toxin that selectively inhibits fast Na(+) channel inactivation) upon removal of extracellular Na(+). Our results suggest that tityustoxin requires the presence of extracellular Na(+) to produce its typical pharmacological effect on Na(+) channel inactivation kinetics, but not to bind to its site.

Effect of toxin-g from Tityus serrulatus scorpion venom on gastric emptying in rats

The effect of toxin-gamma from Tityus serrulatus scorpion venom on the gastric emptying of liquids was studied in 176 young adult male Wistar rats (2-3 months of age) divided into subgroups of 8 animals each. Toxin-gamma was injected i.v. at doses of 25, 37.5, 50 or 100 micrograms/kg and the effect on gastric emptying was assessed 30 min and 8 h later. A time-course study was also performed by injecting 50 micrograms of toxin-gamma/kg and measuring the effect on gastric emptying at times 0.25, 0.5, 1, 2, 4, 8, 24 and 48 h post-venom. Each envenomed animal was paired with its saline control and all received a saline test meal solution containing phenol red (60 micrograms/ml) as a marker. Ten minutes after administering the test meal by gavage the animals were sacrificed and gastric retention was determined by measuring the residual marker concentration of the test meal. A significant delay in gastric emptying, at 30 min and 8 h post-venom, was observed only after 50 and 100 micrograms of toxin-gamma/kg compared to control values. The responses to these two doses were significantly different after 8 h post-venom. Toxin-gamma (50 micrograms/kg) significantly delayed the gastric emptying of liquids at all times studied, with a peak response at 4 h after toxin administration compared to control values. These results indicate that the i.v. injection of toxin-gamma may induce a rapid, intense and sustained inhibition of gastric emptying 0.25 to 48 h after envenomation.

Pharmacological evidence that neuropeptides mediate part of the actions of scorpion venom on the guinea pig ileum

Severe human scorpion envenoming is characterised by instability of several physiological systems and death. These manifestations are explained by the ability of the venom toxins to activate sodium channels in nerve terminals with the subsequent release of neurotransmitters, specially acetylcholine and noradrenaline. However, there is evidence to suggest that other neurotransmitters are also released. We now have sought evidence for a role of the substance P receptor, the tachykinin NK1 receptor, in mediating part of the contractile actions of Tityus serrulatus venom on the isolated guinea pig ileum. Scorpion venom induced a significant elevation of baseline tension with frequent and periodic superimposed contractions on the elevated baseline. Pretreatment with atropine partially blocked the elevation in baseline and in the number of superimposed contractions. These responses were also partially inhibited by the tachykinin NK1 receptor antagonist, CP96,345 (the dihydrochloride salt of (2S,3S)-cis-2-(diphenylmethyl)-N-((2-methoxyphenyl)methyl)-1-az abicycol[2.2.2]octan-3-amine), but not by its inactive enantiomer, CP96,344 (the 2R-3R enantiomer of CP96,345). Pretreatment with the combination of atropine and CP96,345 completely inhibited the effects of the venom. Moreover, pretreatment with the combined drugs abolished the effects of toxin gamma, a toxin purified from the venom. Finally, another tachykinin NK1 receptor antagonist, RP67,580 ((3aR, 7ar)-7,7-diphenyl-2-[1-imino-2-(2-methoxy-phenyl)ethyl]perhydro isoindol-4-one), significantly inhibited the venom-induced contractions. These results demonstrate an important role for NK1 receptors in mediating part of the contractile effects of the venom on guinea pig ileum. The release of neuropeptides may play an important role in the systemic manifestations of severe envenoming.

Role of lysine and tryptophan residues in the biological activity of toxin VII (Ts gamma) from the scorpion Tityus serrulatus

Toxin VII (TsVII), also known as Ts gamma, is the most potent neurotoxin in the venom of the Brazilian scorpion Tityus serrulatus. It has been purified to homogeneity using a new fast and efficient method. Chemical modification of TsVII with the tryptophan-specific reagent o-nitrophenylsulfenyl chloride yielded three modified derivatives (residues Trp39, Trp50 and Trp54). Acetylation of TsVII mostly generated the monoacetylated Lys12 derivative. No side reactions were detected, as indicated by endoproteinase Lys-C peptide mapping, Edman degradation and electrospray mass spectrometry. Circular dichroism and fluorimetric measurements showed that none of the chemical modifications altered the overall structure of the derivatives. The acetylation of Lys12 or the sulfenylation of Trp39 or Trp54 led to a loss of both toxicity in mice and apparent binding affinity for rat brain and cockroach synaptosomal preparations. Sulfenylation of Trp50, however, moderately affected the toxicity of TsVII in mice and had almost no effect on its binding properties. A 3-dimensional model of TsVII was constructed by homology modeling. It suggests that the most reactive residues (Lys12 and Trp39 and Trp54) are all important in the functional disruption of neuronal sodium channels by TsVII, and are close to each other in the hydrophobic conserved region.

Effects of crude venom, tityustoxin and toxin Ts-gamma from Tityus serrulatus scorpion on secretion and structure of the rat submandibular gland

Changes in the rat submandibular glands after intravenous injections of Tityus serrulatus scorpion venom, tityustoxin or toxin Ts-gamma were studied histologically and morphometrically. The acini and the granular convoluted tubules presented the most prominent changes. The following variables were measured: (a) relative volume occupied by the glandular structures; (b) diameter of the granular convoluted tubules and thickness of their epithelium; (c) diameter of the acini. The cytoplasm of the acinar cells was extensively occupied by large confluent vacuoles and had a reduced number of secretory granules after intravenous injections of venom or toxins. The morphological changes caused by toxin Ts-gamma were greater than those evoked by tityustoxin or crude venom injections. In spite of the changes in acinar cells, acinar diameter showed no significant alterations after venom or toxin injections. Reduction of diameter and depletion of the cytoplasmic secretory granules were observed in the granular convoluted tubules 2 h after intravenous injections of crude venom, or after 1 h with tityustoxin or toxin Ts-gamma. The intravenous injection of crude venom did not induce any visible change in the granular convoluted tubules after 1 h. These structural changes could explain the concomitant intense sialagogue effect elicited by crude venom, tityustoxin and toxin Ts-gamma. The sialagogue effect induced by toxin Ts-gamma was larger than those induced by crude venom or tityustoXin.

Alpha- and beta-scorpion toxins evoke glutamate release from rat cortical synaptosomes with different effects on [Na+]i and [Ca2+]i

Scorpion toxins have long been used as tools in the investigation of neurotransmitter release mechanisms. We have used rat cortical synaptosomes to study the effects of a beta-type scorpion toxin (TiTX-gamma) on the release of glutamate and on the concentrations of free sodium and calcium ions inside the synaptosomes. The effects are compared with those of an alpha-type scorpion toxin (TsTX), on which there have been more studies. TsTX increased overall internal sodium and calcium ion concentrations and glutamate release in an incremental, dose dependent manner. TiTX-gamma similarly evoked glutamate release in an incremental, dose dependent manner. However, TiTX-gamma caused little increase in the overall internal sodium and calcium ion concentrations at low doses that evoked a significant release of glutamate and a maximal increase in these ions at somewhat higher doses. The results suggest that TiTX-gamma preferentially binds sodium channels close to the active zones for glutamate release and indicates that modifications of the activation or inactivation of the Na+-channel can lead to very different changes in the cytosolic concentrations of free Na+and Ca2+, with consequences for neurotransmission. This provides an interesting perspective concerning modulation of neurotransmitter release via pharmacological manipulation of Na+-channel properties, that may lead to a better comprehension of its physiological and pathological roles.

Synergism between toxin-gamma from Brazilian scorpion Tityus serrulatus and veratridine in chromaffin cells

Toxin-gamma (Tgamma) from the Brazilian scorpion Tityus serrulatus venom caused a concentration- and time-dependent increase in the release of norepinephrine and epinephrine from bovine adrenal medullary chromaffin cells. Tgamma was approximately 200-fold more potent than veratridine judged from EC50 values, although the maximal secretory efficacy of veratridine was 10-fold greater than that of Tgamma (1.2 vs. 12 microg/ml of catecholamine release). The combination of both toxins produced a synergistic effect that was particularly drastic at 5 mM extracellular Ca2+ concentration ([Ca2+]o), when 30 microM veratridine plus 0.45 microM Tgamma were used. Tgamma (0.45 microM) doubled the basal uptake of 45Ca2+, whereas veratridine (100 microM) tripled it. Again, a drastic synergism in enhancing Ca2+ entry was seen when Tgamma and veratridine were combined; this was particularly pronounced at 5 mM [Ca2+]o. Veratridine induced oscillations of cytosolic Ca2+ concentration ([Ca2+]i) in single fura 2-loaded cells without elevation of basal levels. In contrast, Tgamma elevated basal [Ca2+]i levels, causing only small oscillations. When added together, Tgamma and veratridine elevated the basal levels of [Ca2+]i without causing large oscillations. Tgamma shifted the current-voltage (I-V) curve for Na+ channel current to the left. The combination of Tgamma with veratridine increased the shift of the I-V curve to the left, resulting in a greater recruitment of Na+ channels at more hyperpolarizing potentials. This led to enhanced and more rapid accumulation of Na+ in the cell, causing cell depolarization, the opening of voltage-dependent Ca2+ channels, and Ca2+ entry and secretion.

Behavioral, electroencephalographic, and histopathologic effects of a neuropeptide isolated from Tityus serrulatus scorpion venom in rats

The effects of intrahippocampal administration of a neuropeptide (TS-8F toxin) isolated from Tityus serrulatus scorpion venom have been determined on behavior, limbic seizures, and neuronal degeneration in rats. Behavioral observation showed orofacial automatism, wet dog shakes, and myoclonus. Concomitantly, the electroencephalographic record showed high-frequency and high-voltage spikes that evolved to seizure activity in the hippocampus and cortex. Seven days after TS-8F toxin microinjection, neuronal damage was observed in CA1 and CA2 pyramidal cells and in granular cells of the dentate gyrus. The results suggest that TS-8F toxin may be responsible, at least in part, by the epileptic effects observed with the crude venom. Thus, this toxin may be a useful tool in the study of some neurobiological process.

A rapid procedure for the isolation of the Lys-49 myotoxin II from Bothrops moojeni (caissaca) venom: biochemical characterization, crystallization, myotoxic and edematogenic activity

Bothtrops moojeni snake venom was fractionated on a CM-Sepharose column which was previously equilibrated with 0.05 M ammonium bicarbonate buffer at pH 8.0 and subsequently eluted with an ammonium bicarbonate concentration gradient from 0.05 to 0.5 M at constant pH (8.0) and temperature (25 degrees C). The fraction which eluted last (M-VI) showed, after direct lyophilization, a single band by polyacrylamide gel electrophoresis (PAGE) and SDS-PAGE, indicating an approximate Mr of 14000 and 27000, in the presence and absence of dithiothreitol, respectively. Its amino acid composition revealed a high level of hydrophobic and basic amino acids as well as 14 half-cystine residues. Its isoelectric point and extinction coefficient (E(1.0 mg/ml) (1.0 cm) at 278 nm and pH 7.0) were 8.2 and 1.170, respectively. M-VI was devoid of phospholipase A2 (PLA2) activity on egg yolk, as well as of hemorrhagic, anticoagulant and coagulant activities, but could induce drastic necrosis on skeletal muscle fibres as well as rapid and transient edema on the rat paw. Its N-terminal sequence: SLFELGKMILQETGKNPAKSYGVYGCNCGVGGRGKPKDATDRCCYVHKCCYK... revealed high homology with other Lys 49 PLA2-like myotoxins from other bothropic venoms. Orthorhombic crystals of M-VI, which diffracted to a maximal resolution of 1.6 A, were obtained and indicated the presence of a dimer in the asymmetrical unit.