Mu-conotoxins block voltage-gated sodium channels (Nav) (By similarity). Intraperitoneal injection into fish (1 nmol) provokes weakening and difficulty in swimming after 20 min. Expressed by the venom duct. The cysteine framework is III (CC-C-C-CC). Classified in the M-4 branch, since 4 residues stand between the fourth and the fifth cysteine residues. Monoisotopic mass. Authors confirmed the assignment of this toxin to the M superfamily by cDNA sequencing. Belongs to the conotoxin M superfamily.