What is oxyanion hole?

An oxyanion hole is a pocket or crevice in the active site of an enzyme where the negative charge of an oxyanion transition state intermediate can be stabilized through hydrogen bonding with nearby amino acid residues. This stabilization helps to lower the activation energy of the reaction and increase the efficiency of the enzyme-catalyzed reaction.

The oxyanion hole is often found in enzymes that catalyze reactions involving ester bonds or phosphate groups, which are prone to forming oxyanion intermediates during the reaction. Examples of enzymes that contain an oxyanion hole include serine proteases, such as chymotrypsin and trypsin, as well as acetylcholinesterase and enolase.

The oxyanion hole is typically formed by several amino acid residues, such as serine, threonine, and tyrosine, which are capable of forming hydrogen bonds with the oxyanion intermediate. These residues are often located near the active site of the enzyme and are highly conserved among related enzymes.

Overall, the presence of an oxyanion hole in enzymes is essential for their catalytic activity and plays a crucial role in stabilizing reactive intermediates during the enzymatic reactions.