Biochemistry—Proteolysis Specificity A peptide Val-Lys-Glu-Met-Ser-Trp-Arg-Ala is digested with chymotrypsin. Which fragment set is expected from specific cleavage at aromatic residues?

Introduction / Context:
Proteases recognize specific side chains and cleave peptide bonds adjacent to them. Chymotrypsin preferentially cleaves on the carboxyl side of aromatic residues (Phe, Trp, Tyr). This problem tests your understanding of sequence-specific proteolysis.

Given Data / Assumptions:

• Peptide sequence: Val-Lys-Glu-Met-Ser-Trp-Arg-Ala.
• Enzyme: chymotrypsin (cleaves after aromatic residues).
• Assume a single, ideal cleavage at the most prominent aromatic site.

Concept / Approach:
Locate aromatic residues in the sequence and cleave after that residue. Among the residues, Trp (tryptophan) is aromatic and a prime chymotrypsin target.

Step-by-Step Solution:

Verification / Alternative check:
Trypsin would cleave after Lys and Arg instead, yielding a different pattern. Because the enzyme is chymotrypsin, the Trp site dominates, matching the chosen answer.

Why Other Options Are Wrong:

• Multiple tiny fragments (e.g., splitting at Lys or Arg) reflect trypsin-like, not chymotryptic specificity.
• Cleavage before Trp or at non-aromatic residues does not match chymotrypsin's preference.
• Splitting after Met or Ser is not characteristic of chymotrypsin under standard conditions.

Common Pitfalls:
Confusing chymotrypsin with trypsin; forgetting that cleavage is after the target residue; overlooking that only one aromatic residue exists here.

Final Answer:
Val-Lys-Glu-Met-Ser-Trp + Arg-Ala