Thermolysin is a protease that can cleave peptides at the N-terminal side of branched alkyl residues. Which of the following peptides has the most thermolysin cleavage sites?

Question

Thermolysin is a protease that can cleave peptides at the N-terminal side of branched alkyl residues.  Which of the following peptides has the most thermolysin cleavage sites?

Quizplus · Accepted Answer

11ecba2d_0e60_c413_a3bf_23e8d9d401fb_MD0008_00 The amino acid residues in a peptide can be classified by their general properties. Proteases cleave peptide bonds at specific sites by recognizing residues with specific properties. They may cleave the bond on the N-terminal side of the residue (the side that is closest to the N-terminus of the peptide), or they may cleave the bond on the C-terminal side of the recognized residue (the side that is closest to the C-terminus). For example, trypsin cleaves bonds on the C-terminal side of positively charged residues (R, K), and chymotrypsin cleaves bonds on the C-terminal side of large aromatic residues (F, Y, W). The question states that thermolysin can cleave peptide bonds at the N-terminal side of branched alkyl residues. Leucine (L), isoleucine (I), and valine (V) are the only amino acids with branched alkyl side chains, and the peptide with the most L, I, and V residues will have the most cleavage sites. The peptide HQICSVGPKLNT has three thermolysin cleavage sites, one each of L, I, and V, and more than any of the other choices given. (Choice B) The peptide DNKGSTVYQRWC has only one thermolysin cleavage site at valine. (Choice C) The peptide GHPTLDQIWCER has only two thermolysin cleavage sites, one at leucine and one at isoleucine. (Choice D) The peptide RTHCQGYNESDK does not have any L, I, or V residues, and it has no thermolysin cleavage sites. Educational objective: Amino acids have side chains with specific properties. Side chains with similar properties may be recognized by the same enzyme. Leucine, isoleucine, and valine are hydrophobic amino acids with branched alkyl chains.

Thermolysin Is a Protease That Can Cleave Peptides at the N-Terminal