Question

Can the peptide

Ser-Glu-Pro-Ile-Met-Ala-Pro-Val-Glu-Tyr-Pro-Lys

be hydrolyzed by chymotrypsin? our teacher indicates that it can, but i was under the impresion that if proline was the next amino acid, then the reaction would not go.

Answer 1

Chymotryosin acts in the peptide at the carboxyl side of aromatic amino acid unless the next amino acid is proline. The aromatic amino acids are tyrosine, tryptophan, phenylalanine.

There will be no action occur by chymotrypsin, when proline is next amino acid because chymotrypsin shows it's action via it's catalytic triad which consists of aspartate, histidine and serine. When proline is next amino acid, then catalytic triad is non functional in nature because the imino group of proline has Nitrogen atom which contains positive charge, this will interacts with catalytic triad and makes the enzyme inactive.

There is found aromatic amino acid but the proline is the next amino acid to tyrosine. That's why above peptide can not be hydrolyzed by chymotrypsin.