During Edman degradation, what is the purpose of PITC?

In the context of Edman degradation, PITC (phenylisothiocyanate) plays a crucial role by specifically labeling the N-terminus of the amino acid in a peptide chain. This labeling is essential because Edman degradation is a method used for sequencing amino acids in proteins by identifying the terminal residue step by step.

In this process, PITC reacts with the free amino group of the N-terminal amino acid, forming a cyclic phenylthiohydantoin (PTH) derivative. This derivative is then stable enough to be separated from the rest of the peptide, allowing for its identification through chromatography. As each N-terminal amino acid is identified, the remaining peptide chain can be sequentially processed in the same manner.

This distinct role of PITC is vital for the accuracy and efficiency of Edman degradation, emphasizing its importance in protein sequencing.