Which of the following method is used for the analysis of the C-terminal end of a polypeptide?
## Core Concept
The analysis of the C-terminal end of a polypeptide involves determining the amino acid sequence at the carboxyl-terminal end of a protein. This is a crucial aspect of protein structure elucidation. Various methods are employed to analyze the C-terminal end, including chemical and enzymatic techniques.
## Why the Correct Answer is Right
The correct answer, **Carboxypeptidase**, is an enzyme used for the analysis of the C-terminal end of a polypeptide. Carboxypeptidase is a pancreatic exopeptidase that hydrolyzes peptides at the carboxy-terminal (C-terminal) end. It cleaves the peptide bond at the C-terminal, releasing the C-terminal amino acid. This sequential removal of amino acids from the C-terminal end allows for the determination of the C-terminal sequence of a polypeptide.
## Why Each Wrong Option is Incorrect
- **Option A: Edman degradation** is a method used for determining the N-terminal amino acid sequence of a protein, not the C-terminal. It involves the selective removal of the amino-terminal residue from a peptide or protein.
- **Option B: Cyanogen bromide (CNBr) cleavage** is a chemical method used to cleave peptide bonds at methionine residues. This method does not specifically target the C-terminal end but rather cleaves the protein at specific internal sites.
- **Option C: Trypsin digestion** is an enzymatic method used to cleave peptide bonds at the carboxyl side of the amino acids lysine and arginine, except when either is followed by proline. While useful for generating peptide fragments for sequencing, it does not specifically analyze the C-terminal end.
## Clinical Pearl / High-Yield Fact
A key point to remember is that **Carboxypeptidase** is specifically used for C-terminal analysis, whereas **Edman degradation** is used for N-terminal sequencing. Understanding the specificity of these methods is crucial for protein structure analysis.
## Correct Answer: D. Carboxypeptidase.