A protein has been sequenced after cleavage of disulfide bon

A protein has been sequenced after cleavage of disulfide bonds. The protein is known to contain 3 Cys residues, located as shown below. Only one of the Cys has a free -SH group and the other two are involved in an - S - S- bond. The only methionine and the only aromatic amino acid (Phe) in this protein are in the positions indicated. Cleavage of the intact protein (i.e., with disulfide bonds intact) by either cyanogen bromide or chymotrypsin does not break the protein into two peptides. Where is the -S - S- bond (i.e., AB, BC, or AC)? AC BC AB

Solution

-s-s- bond must be at AC site as,

Cyanogen Bromide cleaves peptide at Methonine Site and Chymotripsin cleaves peptide at Phenylalanine site, if both of this chemicals couldn’t break the protein into two peptides, then AC linkage must be there which holds two peptides intact incase of use of any one of the chemicals mentioned above