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Makatoxin I, a novel toxin isolated from the venom of the scorpion Buthus martensi Karsch, exhibits nitrergic actions

Journal of Biological Chemistry 272(13): 8320-8324

Makatoxin I, a novel toxin isolated from the venom of the scorpion Buthus martensi Karsch, exhibits nitrergic actions

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 GRDAYIADSENCTYTCALNPYCNDLCTKNGAKSGYCQ WAGRYGNACWCIDLPDKVPIRISGSCR. 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 micrograms/ml) markedly relaxed the carbachol-precontracted ACM; the relaxation was inhibited by the stereoselective inhibitor of nitric oxide synthase, N omega-nitro-L-arginine methyl ester (50 micromolar). Thus, MkTx I is the first alpha-toxin that can mediate nitrergic responses in the rat isolated ACM.

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Accession: 002889207

PMID: 9079654

DOI: 10.1074/jbc.272.13.8320

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