Trypsin cleaves peptide bonds on the carboxyl side of which amino acid among the following?

• A. Glycine
• B. Arginine
• C. Proline
• D. Leucine

Answer: (B)

Trypsin has a preference for cutting peptide bonds after basic, positively charged amino acids. Its active site contains a negatively charged pocket that strongly interacts with the side chains of lysine and arginine, with arginine fitting especially well due to its bulky, positively charged guanidinium group. This is why the bond after arginine is the one most commonly cleaved by trypsin.

Glycine and leucine lack that basic side chain, so they aren’t recognized as typical cleavage sites for trypsin. Proline, while it’s an amino acid, often blocks cleavage because its rigid ring structure disrupts the geometry needed for efficient cutting by trypsin, especially if it appears directly after the target site. So, among the options, arginine is the residue after which trypsin most reliably cleaves.