Disulfide isomers of BuIA. (A) A schematic representation of the ribbon, globular and beads disulfide connectivities of BuIA, a conotoxin having the unique 4/4 loop spacing. (B) HPLC traces of ribbon and globular BuIA. Analytical HPLC was carried out using a C18 Phenomenex analytical column (250 × 4.6 mm) with 90% acetonitrile and 0.043% trifluroacetic acid as the eluting solvent B and 1% B per minute as the gradient. Ribbon BuIA elutes earlier than the globular form but has a slightly broadened peak under the conditions utilized.