Question

In the acylation step of the chymotrypsin mechanism, what is the role of an alkoxide?

1) It acts as a nucleophile, attacking the carbonyl carbon of the acyl-enzyme intermediate.
2) It acts as a leaving group, facilitating the departure of the acyl group.
3) It acts as a catalyst, speeding up the reaction rate.
4) It acts as a stabilizer, preventing the formation of unwanted side products.

Answer 1

The alkoxide in chymotrypsin's acylation step acts as a nucleophile, attacking the carbonyl carbon to facilitate peptide bond cleavage.

Step-by-step explanation:

In the acylation step of the chymotrypsin mechanism, the role of an alkoxide is to act as a nucleophile. The alkoxide is formed when the serine hydroxyl group on the enzyme is turned into a more reactive form by the removal of a hydrogen atom, thus increasing its nucleophilicity. This alkoxide group then attacks the carbonyl carbon of the acyl-enzyme intermediate, helping to form a tetrahedral intermediate that is key in the acylation process. The objective is to facilitate the cleavage of the peptide bond that is being targeted by chymotrypsin.