L leucine d10

Leucine (L-leucine-¹³C, L-leucine-¹³C₆,¹⁵N, and L-leucine-D₁₀), glycine (glycine-d₂ and glycine-¹³C₂,¹⁵N), heavy formaldehyde (CD₂O), sodium cyanoborodeuteride were purchased from Cambridge Isotope Laboratories, Inc. (Tewksbury, MA). Acetic acid (AA), acetonitrile (ACN), dimethyl sulfoxide (DMSO), formic acid (FA), methanol (MeOH), and water were purchased from Fisher Scientific (Pittsburgh, PA). Sodium cyanoborohydride, sodium meta-periodate, triethylammonium bicarbonate buffer (TEAB, 1.0 M) and tris(2-carboxy-ethyl) phosphine hydrochloride (TCEP) were purchased from Sigma-Aldrich (St. Louis, MO). PNGase F was purchased from Promega (Madison, WI). Oasis HLB 1cm³ cartridges were purchased from Waters Corporation (Milford, MA). Bovine thyroglobulin (BTG) and human serum protein (HSP) were purchased from Thermo Fisher Scientific (Rockford, IL). Microcon-30kDa centrifugal filters (30K MWCO) were purchased from Merck Millipore Ltd. (Darmstadt, Germany). PolyGLYCOPLEX A™ beads (3 μm) were purchased from PolyLC Inc. (Columbia, MD). Fused silica capillary tubing (inner diameter 75 μm, outer diameter 375 μm) was purchased from Polymicro Technologies (Phoenix, AZ). All reagents were used without additional purification.