title: Charybdotoxin and noxiustoxin, two homologous peptide inhibitors of the K+ (Ca2+) channel.
abstract: We show that noxiustoxin (NTX), like charybdotoxin (CTX) described by others, affects Ca2+-activated K+ channels of skeletal muscle (K+(Ca2+) channels). Chemical characterization of CTX shows that it is similar to NTX. Although the amino-terminal amino acid of CTX is not readily available, the molecule was partially sequenced after CNBr cleavage. A decapeptide corresponding to the C-terminal region of NTX shows 60% homology to that of CTX, maintaining the cysteine residues at the same positions. While CTX blocks the K+ (Ca2+) channels with a Kd of 1-3 nM, for NTX it is approx. 450 nM. Both peptides can interact simultaneously with the same channel. NTX and CTX promise to be good tools for channel isolation.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D018999:Charybdotoxin; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008051:Lipid Bilayers; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000502:physiology; D012604:Scorpion Venoms / Q000302:isolation & purification / Q000494:pharmacology*
chemical_list: D007473:Ion Channels; D008051:Lipid Bilayers; D012604:Scorpion Venoms; D018999:Charybdotoxin; C052567:noxiustoxin; D002118:Calcium