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.
A terminal cysteine residue plays a role analogous to that of a cysteine within a catalytic trio. The free N terminus acts as a base to activate the nucleophile and deprotonate the leaving group during hydrolysis, specifically with ammonia serving as the departing molecule.