Chemicals and Reagents.
Phosphate-buffered saline (PBS) tablets, LC/MS grade water 0.1% formic acid, methanol and acetonitrile 0.1% formic acid were from Fisher Scientific (PA). Deuterium oxide (99.9%) was from Cambridge Isotope Laboratories (MA). Urea and tris(carboxyethyl)phosphine (TCEP) were from Sigma-Aldrich (MO). Reagent and sample vials for HDX-MS were from Trajan Scientific and Medical (NC) and Thermo Scientific (CA), respectively.