Figure 1.

Examples of reaction diversity in the pentein superfamily. A) Hydrolases, typified here by dimethylarginine dimethylaminohydrolase (DDAH), form a thiouronium intermediate after loss of the substrate’s N^ω-substitutent, and subsequently hydrolyze the intermediate to yield a ureido-containing product. B) Amidinotransferases, typified here by Arg:Gly amidinotransferase, form a chemically similar thiouronium intermediate after loss of the N^δ-substitutent, and subsequently catalyze amidinotransfer to an acceptor amine. C) Dihydrolases, typified here by N^α-succinyl-L-arginine dihydrolase, have been proposed to catalyze their hydrolytic reactions through similar thiouronium intermediate(s), but a covalent adduct has not yet been detected experimentally.