Blocks specifically voltage-activated potassium channels (Kv) of the Shaker family (IC(50)=1.33 nM). Expressed by the venom duct. Contains 2 disulfide bonds instead of 3, as for all Kunitz domain proteins. A double Cys-mutant carrying an additional Cys bridge does not show difference in activity with the natural peptide. However, there are some differences in the kinetics of binding of both peptides to the channel (PubMed:15833744). Belongs to the venom Kunitz-type family.