Covalent DDAH inactivation by ebselen. (A) Product formation of P. aeruginosa DDAH incubated in the absence (▸, 1 mM dimethylarginine) and presence of ebselen (0.64 μM) at varying dimethylarginine (ADMA) concentrations [1 (◂), 1.5 (⧫), 2 (◼), 3 (▼), 4 (●), and 6 mM (▲)]. (B) Dependence of observed inactivation rates kobs/[I] fits to a hyperbola with inactivation rates of 43000 ± 7000 M–1 s–1 for free enzyme and 400 ± 300 M–1 s–1 for substrate-bound enzyme. (C) Structure of ebselen. (D) Structure of proposed inhibitory adduct with the active site Cys.