Imperatoxin

Ryanodine receptors are found in neurons, exocrine cells, smooth muscle cells and trigger the release of Ca²⁺ from intracellular Ca²⁺ pools. These receptors are essential for maintaining intracellular Ca²⁺ homeostasis in cardiac and skeletal muscles. A 33-residue peptide, imperatoxin A (IpTxa), was isolated from scorpion venom (Pandinus imperator) and may be useful as a ryanodine receptor probe. IpTxa increased [³H]ryanodine binding in a dose-dependent manner with an ED₅₀ value of 0.016 µg/ml.
Valdivia, H. H., Kirby, M. S., Lederer, W. J. and Coronado, R. Proc. Natl. Acad. Sci. USA, 89, 12185 (1992). (Pharmacology)
El-Hayek, R., Lokuta, A. J., Arévalo, C. and Valdivia, H. H. J. Biol. Chem., 270, 28969 (1995). (Pharmacology)
Zamudio, F. Z., Gurrola, G. B., Arévalo, C., Sreekumar, R., Walker, J. W., Valdivia, H. H. and Possani, L. D. FEBS Lett., 405, 385 (1997). (Original-Structure)

Imperatoxin A (IpTxa)
(Scorpion, Pandinus imperator)
Gly-Asp-Cys-Leu-Pro-His-Leu-Lys-Arg-Cys-Lys-Ala-
Asp-Asn-Asp-Cys-Cys-Gly-Lys-Lys-Cys-Lys-Arg-Arg
-Gly-Thr-Asn-Ala-Glu-Lys-Arg-Cys-Arg (Disulfide bonds undetermined)
M.W. 3758.4 C₁₄₈H₂₅₄N₅₈O₄₅S₆
Activator of Ca²⁺ Release Channels/Ryanodine Receptors

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