Figure 33.4: Disruption of disulphide bond by different approaches.

Stage 2. Cleavage of the polypeptide chain: Proteases and the chemical agents targeting proteins have a specific recognition sequence and they cleave after a particular amino acid. A list of protease and chemicals commonly used to digest the polypeptides into the small peptide fragment is given in Table 38.1.

Table 33.1: Some Common reagents for fragmenting polypeptide chain.
S.No	Reagent	Cleavage Point
1	Trypsin	After Lys, Arg
2	Chymotrypsin	After Phe, Trp, Tyr
3	Pepsin	After Leu, Phe, Trp, Tyr
4	Cynogen Bromide	After Met

Stage 3. Sequencing the peptides-Once the peptide fragments are generated, we can start the sequencing of each polypeptide chain. It has following steps:
A. Identifying the N-terminal residue: The N-terminal amino acid analysis is a 3 steps process.