BIOMOLECULES AND ENZYMES

Detailed explanation-1: -The Edman degradation is by far the most important method in sequence analysis. It involves stepwise degradation of peptides with phenyl isothiocyanate, starting at the N-terminus of the polypeptide. The resultant phenylthiohydantoin is either identified directly or the amino acid is recovered.

Detailed explanation-2: -Phenyl isothiocyanate is reacted with an uncharged N-terminal amino group, under mildly alkaline conditions, to form a cyclical phenylthiocarbamoyl derivative. Then, under acidic conditions, this derivative of the terminal amino acid is cleaved as a thiazolinone derivative.

Detailed explanation-3: -Phenyl isothiocyanate (PITC) is a reagent used in reversed phase HPLC. PITC is less sensitive than o-phthaldehyde (OPA) and cannot be fully automated. PITC can be used for analysing secondary amines, unlike OPA. It is also known as Edman’s reagent and is used in Edman degradation.

Detailed explanation-4: -The reagent used in the Edman degradation is phenyl isothiocyanate. You may find it helpful to review the relationship between cyanates, isocyanates, thiocyanates and isothiocyanates. You need not memorize the specific peptide bonds that are broken by the enzymes trypsin and chymotrypsin.

Detailed explanation-5: -In the Edman degradation, the polypeptide is treated with phenylisothiocyanate-the Edman reagent-which reacts with the N-terminal amino acid to give an N-terminal PTC derivative of the protein.