Suggested mechanism of the BiuH.

<p>Lys142 stabilizes Asp36 that will act as a general base and deprotonate Cys175, allowing Cys175 to perform a nucleophilic attack on the carbonyl end of biuret. Cys175 then binds to biuret forming a tetrahedral intermediate. Asp36 then acts as a general acid, leading to the collapse of the intermediate and the production of an ammonia and a thioester intermediate. Following the addition of a water molecule, Asp36 deprotonates the molecule of water leading to the hydrolysis of the thioester intermediate, forming a new tetrahedral intermediate. Finally, the enzyme is restored to its original state, releasing the allophanate product.