Location of the disulfide bonds in the antitumor protein neocarzinostatin

Two disulfide bonds in the antitumor antibiotic neocarzinostatin were determined chemically. The peptic and peptic/thermolytic peptides from the native protein were isolated by gel filtration and ion-exchange chromatography followed by reverse-phase HPLC. The cystine peptides obtained were oxidized separately by performic acid treatment and further separated by HPLC into cysteic acid peptides. Sequence analyses of the isolated peptides revealed the location of the disulfide bonds at Cys37-Cys47 and Cys88-Cys93.