Each enzyme was diluted in pH 7.5 Tris buffer to achieve a final concentration 500 nM after addition of compound. Enzymes were pretreated by adding 2 μL of compound stock to 198 μL of enzyme solution. Unless otherwise specified, the final concentration of each compound was 100 μM. After one hour, the mixture was injected onto a BEH C8 column (Waters) on a UPLC-MS system (Xevo QToF, Waters). Reverse-phase liquid chromatography was carried out with gradient of 5% to 95% of acetonitrile (with 0.02% formic acid) for 8.5 min. The protein typically eluted around 4 min; this peak on the chromatogram was integrated and deconvoluted using the MaxEnt1 algorithm. Subsequently, peaks were chosen according to the theoretical MW of each adduct, within a range of 5 Da, and integrated for the signal intensity ± 1 Da. The abundance of each detectable enzyme species was normalized to the total intensity of all enzyme species.