Assays

LCL cells were cultured in lysine- and arginine-free DMEM (GIBCO) supplemented with 2 mM glutamine, 10% dialyzed FBS and antibiotics as well as with 146 mg/ml light (K0, Sigma) or heavy lysine (K8, Cambridge Isotope Laboratories) and 84 mg/ml light (R0, Sigma) or heavy (R10, CambridgeIsotope Laboratories) arginine, respectively. Cell pellets were lysed in 8 M Urea in 50 mM Tris-HCl pH 8.0. Protein concentrations were determined by a BCA assay and protein amounts were adjusted to equal concentrations. ...