Question

Edman degradation reaction is used in identifying

• A. N-terminal amino acids
• B. C-terminal amino acids
• C. Lipids
• D. Carbohydrates

Hint:

Protein Sequencing Reagents:
N-Terminal Identification = Edman's reagent (PITC), Sanger's reagent (DNFB), Dansyl chloride.
C-Terminal Identification = Carboxypeptidases, Hydrazinolysis.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Pehr Edman's sequential chemical degradation method cleaves and identifies one N-terminal amino acid at a time without hydrolyzing the rest of the polypeptide chain.
Key Formula or Approach:
\[ \text{Polypeptide} + \text{PITC (Phenylisothiocyanate)} \xrightarrow{\text{Mild Alkali}} \text{PTC-Peptide} \xrightarrow{\text{Anhydrous Acid}} \text{PTH-Amino Acid} + \text{Peptide}_{(n-1)} \]

Step 2: Detailed Explanation:
In protein sequencing chemistry:
- Edman Degradation uses Phenylisothiocyanate (PITC Edman's Reagent) to react specifically with the uncharged free $\alpha$-amino group of the N-terminal amino acid under mildly alkaline conditions.
- Treatment with anhydrous trifluoroacetic acid selectively cleaves the first peptide bond, releasing the N-terminal residue as an anilinothiazolinone (ATZ) derivative, which is converted into a stable phenylthiohydantoin (PTH) amino acid and identified by HPLC. The intact shortened peptide undergoes the next cycle.

Step 3: Final Answer:
Hence, Edman degradation is used in identifying N-terminal amino acids, corresponding to option (A).