Which of the following enzymes is an exopeptidase?

Question

BlackTom AI · Accepted Answer

Exopeptidases remove amino acids from the ends of peptide chains, whereas endopeptidases cleave peptide bonds within the interior of the chain.

1. Relevant knowledge points and concepts
- Exopeptidase: enzyme that cleaves terminal peptide bonds, releasing single amino acids or dipeptides from the N- or C-terminus (examples: aminopeptidases, carboxypeptidases).
- Endopeptidase: enzyme that cleaves internal peptide bonds (examples: pepsin, trypsin, chymotrypsin, elastase).
- Specific enzymes listed: Pepsin is an aspartic endopeptidase active in the stomach; Chymotrypsin and Elastase are pancreatic serine endopeptidases acting on internal peptide bonds; Carboxypeptidase is a pancreatic exopeptidase that removes C-terminal residues (e.g., carboxypeptidase A is a zinc metalloprotease).

2. Step-by-step reasoning
- Identify which definition fits each option.
- Pepsin: cleaves internal peptide bonds (preferentially after aromatic residues) in acidic pH → endopeptidase.
- Chymotrypsin: cleaves peptide bonds on the carboxyl side of large hydrophobic/aromatic residues inside the chain → endopeptidase.
- Elastase: cleaves peptide bonds adjacent to small neutral residues (e.g., alanine) inside the chain → endopeptidase.
- Carboxypeptidase: specifically cleaves the C-terminal peptide bond, releasing single amino acids from the C-terminus → exopeptidase.

3. Calculations
- Not applicable; this is conceptual classification (no numerical calculations needed).

4. Why the correct answer is correct
- Carboxypeptidase fits the exopeptidase definition by hydrolyzing peptide bonds at the C-terminal end of polypeptides, producing free carboxy-terminal amino acids. It therefore directly matches the term “exopeptidase.”

5. Why the other options are incorrect
- Pepsin, chymotrypsin, and elastase all cleave internal peptide bonds (endopeptidases), not terminal bonds; thus they are not exopeptidases.

6. Conclusion
- The correct answer is b. Carboxypeptidase, which matches the provided answer.

Which of the following enzymes is an exopeptidase?单项选择题

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