The polymorphism E210A (rs6577) was observed in a single kidney sample (Biorep 3), which was derived from a 53-year-old African American male (Table ). This coding SNP occurs with much higher frequency in Africa Americans (56.5%) compared to the global population (9.9%). Microsomal glutathione S-transferase (MGST) 1, 2, and 3 were observed in the small intestine and lung (1), small intestine and kidney (2), and heart tissue (3), respectively (Figure &). These glutathione transferases are polytopic membrane proteins located in the endoplasmic reticulum membrane with both glutathione conjugation and peroxidase activity. A novel MGST3 proteoform (PFR5719232) that lacks the C-terminal cysteine necessary for S-palmitoylation was the predominant form observed in heart tissue. Enrichment of functionally relevant genes from the identified proteoforms was particularly notable for heart tissue, with terms associated with ATP synthesis and muscle contraction leading the list (Figure ). Six proteoforms of cardiac phospholamban (PLN), a key regulator of cardiac contraction via inhibition of the sarcoplasmic reticulum calcium pump (SERCA), were identified by RPLC-MS/MS (Figure ). While unmodified PLN and palmitoylated PLN have both been reported previously, this study is the first report of phosphorylated PLN and combined phosphorylation and palmitoylation. Phosphorylation and palmitoylation of PLN have both been shown to control the impact localization, complexation, and inhibition of SERCA, so accurate measurement of their combination will help clarify PLN's role in health and disease. We also present evidence for phosphorylation at ~30% stoichiometry of ventricle myosin regulatory light chain (RLCV). Prior reports by the Ge group have established N-terminal trimethylation of RLCV and phosphorylation of swine RLCV, but phosphorylation of human RLCV was unlocalized and observed at <10% stoichiometry. The removal of N-terminal methionine and trimethylation was confirmed by tandem HCD fragmentation, and the site of phosphorylation was localized to S15, which is analogous to the site identified on swine RLCV (Figure ). On a last analytical note, phosproteoforms of cardiac troponin I (cTnI) were not separated by RPLC but were at baseline by CZE (Figure ); proteoform quantitation by both techniques showed <10% coefficient of variation between them. Better separation of the CZE should translate into better on-the-fly sequence coverage and proteoform characterization with tandem MS scan speeds.