Abstract
Buthus martensi Karsch venom exhibits nitrergic action in rat anococcygeus muscle (ACM). We have purified a novel toxin, makatoxin I (MkTx I), which exhibits nitrergic action, to homogeneity from this venom by a combination of gel-filtration, cation-exchange chromatography, and reverse-phase chromatography. Its purity was assessed by capillary electrophoresis and mass spectrometry. Its molecular weight was found to be 7031.71 +/- 2.88 as calculated from electrospray mass spectrographic data. The complete amino acid sequence was elucidated by sequencing of reduced and S-pyridylethylated toxin and a carboxyl-terminal peptide, P55-64, generated by the cleavage of toxin with endoproteinase Lys-C. The complete sequence of MkTx I is GRDAYIADSENCTYTCALNPYCNDLCTKNGAKSGYCQWAGRYGNACWCIDLPDKVPIRISGSCR. This toxin is composed of 64 amino acid residues and contains 8 half-cystine residues. Structurally, MkTx I has high similarity to Bot I and Bot II when compared with toxins from other scorpion species. The effects of MkTx I on nitrergic responses were investigated using the rat isolated ACM mounted in Krebs solution (37 degrees C, 5% CO2 in O2). MkTx I (2 microg/ml) markedly relaxed the carbachol-precontracted ACM; the relaxation was inhibited by the stereoselective inhibitor of nitric oxide synthase, Nomega-nitro-L-arginine methyl ester (50 microM). Thus, MkTx I is the first alpha-toxin that can mediate nitrergic responses in the rat isolated ACM.
Highlights
Scorpion venoms consist of complex mixtures of several toxins that exhibit various pharmacological activities including selective actions at sodium and potassium channels, which are the major molecular targets of scorpion toxins [1]
In a preliminary study we observed that MKV produced relaxant responses of the rat precontracted anococcygeus muscle (ACM), suggesting that some constituent toxin(s) present in MKV could mimic the effects of nitrergic transmission involving the release of the inhibitory neurotransmitter nitric oxide (NO)
We were interested in isolating and purifying the bioactive component(s) present in the venom as well as identifying and characterizing the pure toxin(s) mediating the relaxant responses of the rat ACM. In this communication we report the isolation, purification, and complete amino acid sequence of a novel toxin, makatoxin I (MkTx I), isolated from the venom of B. martensi Karsch and provide the first documentation of some novel nitrergic actions mediated by a scorpion toxin
Summary
Scorpion venoms consist of complex mixtures of several toxins that exhibit various pharmacological activities including selective actions at sodium and potassium channels, which are the major molecular targets of scorpion toxins [1]. Electrophysiological studies indicate that MKV contains some neurotoxic compounds that possibly act on the Na1ϩ channels in the excitable membrane of nerve and muscle [3], cultured mouse cardiomyocyte [4], and rat anterior pituitary cells [5]. We were interested in isolating and purifying the bioactive component(s) present in the venom as well as identifying and characterizing the pure toxin(s) mediating the relaxant responses of the rat ACM. In this communication we report the isolation, purification, and complete amino acid sequence of a novel toxin, MkTx I, isolated from the venom of B. martensi Karsch and provide the first documentation of some novel nitrergic actions mediated by a scorpion toxin
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