Margatoxin, an alpha-KTx scorpion toxin, is a high affinity inhibitor of Kv1.3 (Kd=11.7 pM). Margatoxin inhibits the Kv1.2 (Kd=6.4 pM) and Kv1.1 (Kd=4.2 nM). Margatoxin, a 39 amino-acid-long peptide, is isolated from the venom of the scorpion Centruroides margaritatus and widely used in ion channel research.