Stored-frozen protein samples were buffer exchanged with 5 mM Tris-HCl pH 8.0, 15 mM NaCl buffer using 4K cut-off Amicon® small Centrifugal Filter Units (Millipore Sigma, Burlington, MA, USA) and prepared at 0.1-0.2 mg/mL. 96 µL of this solution was mixed with 4 µL of 2.5 mM inhibitor. Pure DMSO was used as a negative control. Protein samples were analyzed by LC-MS using a Dionex Ultimate 3000 UHPLC coupled to a Bruker Maxis Impact Q-TOF in positive ESI mode. Samples were separated on an Agilent PLRP-S column (1000Å, 5 μM, 2.1 x 50 mm) heated to 80 ⁰C at a flow rate of 0.5 ml/min using a gradient of 80% mobile phase A (0.1% formic acid in H2O) and 20% mobile phase B (0.1% formic acid in ACN) for 2 mins, ramped to