Structure and action of heteronemertine polypeptide toxins: disulfide bonds of Cerebratulus lacteus toxin B-IV.

The positions of the disulfide bonds in Cerebratulus lacteus toxin B-IV were investigated by hydrolysis of the unreduced protein with a variety of proteases. The resulting peptides were purified by gel filtration, ion exchange chromatography, and preparative paper electrophoresis and chromatography. Determination of the amino acid compositions of the cystine-containing peptides purified demonstrated the existence of disulfide bonds linking half-cystine residues 12 and 24, 21 and 51, and 35 and 38. The fourth bond, involving half-cystines 10 and 47, was assigned by difference.