Which of the following reagents specifically react with amino-terminal amino acid present in a peptide?
Show Hint
- Sanger's Reagent: 1-Fluoro-2,4-dinitrobenzene (FDNB)
- Edman's Reagent: Phenyl isothiocyanate (PITC)
Both target the N-terminus of proteins and are fundamental to historical sequencing methods.
Step 1: Understanding the Concept:
Determining the primary sequence of a protein requires identifying the terminal amino acids. Specific chemical reagents are designed to label the free alpha-amino group at the N-terminus of a polypeptide chain. Step 2: Detailed Explanation:
1. 1-Fluoro-2,4-dinitrobenzene (A): Also known as Sanger's reagent, it reacts with the free amino group of the N-terminal amino acid to form a yellow dinitrophenyl-amino acid derivative.
2. Phenyl isothiocyanate (C): Known as Edman's reagent, it reacts with the N-terminal amino acid under mild alkaline conditions, allowing sequential cleavage and identification of N-terminal residues.
3. Ninhydrin (D): Reacts non-specifically with any free primary amino group (such as free amino acids) to produce a purple pigment, and is not a specific N-terminal sequencing reagent.
4. Thus, Sanger's reagent (A) and Edman's reagent (C) are the primary N-terminal labeling chemicals. Step 3: Final Answer:
The correct combination is (A) and (C) only.
