Upgrade to remove ads
Only $2.99/month

Chymotrypsin mechanism

Terms in this set (7)

Step #1
SUBSTRATE BINDING:
-when substrate binds, side chain of the residue adjacent to the peptide bond to be cleaved nestles in a hydrophobic pocket on the enzyme
-positions the peptide bond for attack.
Step #2
NUCLEOPHILIC ATTACK:
-interaction of Ser195 and His57 generates strongly nucleophilic alkoxide ion on Ser195
-the alkoxide ion attacks the peptide carbonyl group, forming a tetrahedral acyl-enzyme.
-this is accompanied by formation of a short-lived negative charge on the carbonyl oxygen of the substrate, which is stabilized by hydrogen bonding in the oxyanion hole.
Step #3
SUBSTRATE CLEAVAGE:
-inability of the negative charge on the substrate carbonyl oxygen leads to collapse of the tetrahedral intermediate
-re-formation of a double bond with carbon displaces the bond between carbon and the amino group of the peptide linkage, breaking the peptide bond.
-the amino leaving group is protonated by His57, facilitating its displacement.
Step #4
WATER COMES IN:
-an incoming water molecule is deprotonated by general base catalysis, generating a strongly nucleophilic hydroxide ion.
-attack of the hydroxide on the ester linkage of the acyl-enzyme generates a second tetrahedral intermediate, with oxygen in the oxyanion hole again taking on a negative charge.
Step #5
WATER ATTACKS:
-collapse of the tetrahedral intermediate forms the second product, a carboxylate anion, and displaces Ser195.
Step #6
BREAK-OFF FROM THE ENZYME:
-collapse of the tetrahedral intermediate forms the second product, a carboxylate anion, and displaces Ser195.
Step #7
PRODUCT DISSOCIATES:
-dissociation of the second product from the active site regenerates free enzyme.
THIS SET IS OFTEN IN FOLDERS WITH...