mbb 222 - chymotrypsin reaction mechanism

who are the “players” in the mechanism? who are the most influential?

Asp102, His57, Ser195, Gly193, substrate

what happens after the substrate has entered and aligned itself?

His57: snatches a H from Ser195

Ser195: now-deprotonated oxygen binds to the carbonyl carbon of the substrate

substrate: in order to accomodate the new bond with Ser195, the double bond of the carbonyl oxygen shifts and becomes a lone pair, being stabilized by H-binding in the oxyanion hole.

what happens in step 3?

His57: donates a proton to the nitrogen of the peptide.

Substrate: in order to accept the proton from His57, the bond between the nitrogen and the carbonyl carbon is cleaved. the carbonyl oxygen double bonds to the carbonyl carbon again.

what happens in step 4?

WATER ENTERS THE ACTIVE SITE

His57: snatches a proton from water

Substrate: carbonyl double bond shifts to become a lone pair on oxygen, and the carbonyl carbon binds to the OH- from the water molecule.

what happens in step 5?

His57: donates a proton to Ser195

Ser195: in order to accept the proton from His57, splits the bond between the oxygen and the carbonyl carbon of the substrate.

substrate: carbonyl double bond is restored, bond is officially cleaves and substrate exits the acitve site.

what happens in step 6?

nothing, meant to show that everything is back to the way it was before