A Kunitz-type toxin specific for mKv1.3/KCNA3 potassium channel. Inhibits currents with an IC50 of 6.2 nM (where 1 µM inhibits 80% of currents). Also has weak inhibitory activity against mKv1.1/KCNA1 (where 1 µM inhibits less than 50% of currents), hKv1.2/KCNA2 (where 1 µM inhibits less than 50% of currents), and hKCa2.3/KCNN3. This toxin shas potential for diagnosing and treating Kv1.3-mediated autoimmune diseases (Chen et al. J. Bio. Chem.).