title: Makatoxin I, a novel toxin isolated from the venom of the scorpion Buthus martensi Karsch, exhibits nitrergic actions.
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.
authors.affiliation: Venom and Toxin Research Group, National University of Singapore, Lower Kent Ridge Road, Singapore 119260, Singapore.
authors.forename: J
authors.initials: J
authors.lastname: Gong
authors.forename: R M
authors.initials: RM
authors.lastname: Kini
authors.forename: M C
authors.initials: MC
authors.lastname: Gwee
authors.forename: P
authors.initials: P
authors.lastname: Gopalakrishnakone
authors.forename: M C
authors.initials: MC
authors.lastname: Chung
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009125:Muscle Relaxants, Central / Q000302:isolation & purification* / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D051381:Rats; D012604:Scorpion Venoms / Q000737:chemistry* / Q000302:isolation & purification* / Q000494:pharmacology; D012605:Scorpions
chemical_list: D009125:Muscle Relaxants, Central; D012604:Scorpion Venoms; C105338:makatoxin I; D009569:Nitric Oxide