Functional analysis of the Mn2+ requirement in the catalysis of ureohydrolases arginase and agmatinase - a historical perspective.

Ureohydrolases form a conserved family of enzymes with a strict requirement for divalent metal ions for catalytic activity. They catalyze the hydrolysis of the guanidino group and produce urea. In their active sites six highly conserved amino acid residues form a binding pocket for two catalytically essential metal ions that are needed to activate a water molecule to initiate the hydrolysis of the guanidino group in a nucleophilic attack. Focus in this review is on two members of the ureohydrolase family, the Mn2+–dependent arginase and agmatinase, which play important roles in functions related to replication and cell survival. We will focus in particular on Mn2+ binding interactions, and on how this metal ion contributes to the reaction catalyzed by these enzymes. We also include the agmatinase-like protein (ALP) because it is functionally closely related to agmatinase, also requires at least one Mn2+ ion for catalytic activity, but may possess an active site that differs significantly from all other known ureohydrolases. The ureohydrolases arginase and agmatinase have two Mn2+ binding sites with differing affinity (site B has the higher affinity). Only one Mn2+ is required for catalysis, but the presence of the second enhances the activity significantly. Unlabelled Image • Ureohydrolases require divalent metal ions for their catalytic function. • Arginase and agmatinase are Mn2+-dependent ureohydrolases. • Both enzymes can accommodate two Mn2+ ions in their active sites. • The two metal ions bind with different affinities to the active site. • Only one Mn2+ is necessary to promote catalysis, but the second one enhances activity. [ABSTRACT FROM AUTHOR]