Chymotrypsin Mechanism

Memory Hack💡

Ser attacks, tetrahedral, collapse, actyl enzyme, water attacks, tetrahedral, collapse, products! 

Notes

What is Chymotrypsin? 

-It is an enzyme that is secreted from the pancreas. It hydrolyzes peptide bonds SELECTIVELY on the carboxyl side of hydrophobic amino acids. 

Let's break this down… 

“Hydrolyzes peptide bonds” means that it breaks peptide bonds (the bonds holding amino acids together) by the addition of a water molecule (hydro-). 

It is selective because it does not just randomly do this to every amino acid, it must be specific! → specifically… a hydrophobic amino acid! If you remember, hydrophobic amino acids are nonpolar.

Its active site is a catalytic triad -All this means is that its active site contains 3 amino acids: Serine 195, Histidine 57, and Aspartate 102 

Chymotrypsin has a “burst” phase followed by a steady state phase. In the BURST phase, chymotrypsin is making a lot of product quickly. In the STEADY STATE phase, the amount of product tapers off, and it slows down. 

This is because of the process of chymotrypsin: 

• Starts with acylation

• Ends with deacylation

Remember the irreversible inhibitors from before? 

DIPF: this is a group specific inhibitor for Serine 195. It ONLY covalently modifies Serine 195, no other serine. 

TPCK: this is an affinity label inhibitor of His57. It modifies His57 in the active state.

These both inhibit the function of chymotrypsin.