Modification of reduced bovine serum albumin by 14C-labeled iodoacetamide. (A) MS/MS relative peptide abundance total ion chromatogram. (B) Peptide fraction collection and SS-AMS analysis. (C) 12C (top) and 14C (bottom) traces from LS-AMS. The following numbered 14C peaks were found by MS/MS to correspond to the following Cys containing peptides: 2, ETYGDMADCCEK; 3, TCVADESHAGCEK and QNCDQFEK; 4, ETYGDMADCCEK and SHCIAEVEK; 7, LKPDPNTLCDEFK and YNGVFQECCQAEDK; 8, RPCFSALTPDETYVPK and SLHTLFGDELCK; 10, GLVLIAFSQYLQQCPFDEHVK and LFTFHADICTLPDTEK. All other numbered peaks have elution times corresponding to more than two Cys-containing peptides.