A terminal cysteine residue acts as the nucleophile in the first part of the reaction, analogous to the cysteine of a catalytic triad. The free N terminus acts as a base to activate the nucleophile and protonate the leaving group in the hydrolytic reaction, in this case ammonia.
In the initial phase of the reaction, a terminal cysteine residue acts similarly to a component of a catalytic triad. The N terminus is utilized as a base to facilitate the nucleophile's activation and protonate the departing molecule, which in this case is ammonia.