In turn, aminic group (-NH3+) of the Ile16 residue interacts with the side chain of Asp194, producing the "oxyanion hole" and the hydrophobic "S1 pocket".

It facilitates the cleavage of peptide bonds by a hydrolysis reaction, which despite being thermodynamically favorable, occurs extremely slowly in the absence of a catalyst.

First, the nucleophilicity of Ser-195 is enhanced by general-base catalysis in which the proton of the serine hydroxyl group is transferred to the imidazole moiety of His-57 during its attack on the electron-deficient carbonyl carbon of the protein-substrate main chain (k1 step).

The buildup of negative charge on the resultant tetrahedral intermediate is stabilized in the enzyme's active site's oxyanion hole, by formation of two hydrogen bonds to adjacent main-chain amide-hydrogens.

However, evidence for similar general-acid catalysis of the k2 reaction (Tet2)[7] has been controverted;[8] apparently water provides a proton to the amine leaving group.

Breakdown of Tet1 (via k3) generates an acyl enzyme, which is hydrolyzed with His-57 acting as a general base  (kH2O) in formation of a tetrahedral intermediate, that breaks down to regenerate the serine hydroxyl moiety, as well as the protein fragment with the newly formed carboxyl terminus.