ABPP can also be used as a competitive screen to identify both reversible and irreversible enzyme inhibitors and also to confirm target inhibition because inhibitors have the ability to block probe labeling of enzymes (Kidd et al., 2001; Greenbaum et al., 2002; Leung et al., 2003; Adibekian et al., 2011) . Competitive ABPP has already led to the discovery of selective serine inhibitors (e.g., carbamates, trizole ureas) for several enzymes (e.g., peptidase, lipases), which have in turn been used to test the function of these proteins in living systems (Bachovchin et al., 2010; Adibekian et al., 2011 ). An alternative omic strategy would be to examine libraries of commercially available protease inhibitors for their ability to inhibit a virus' pathological process; this would potentially lead to development of novel therapeutic options.