Fig. 4.
Identification of mouse serum albumin excreted into the urine of a Tg mouse after DT administration. A SDS–PAGE analysis of urine samples of a Tg mouse before (0) and 1–11 days after DT administration of 50 μg/kg. The CBB-stained protein bands (a to f) were excised. The proteins in gel pieces were digested with trypsin, and the digested peptides were extracted and analyzed by a tandem mass spectrometry. a, b and c were identified as mouse serum albumin; d a mouse major urinary protein, MUP3; e another major urinary protein, MUP1; and f a mouse α2U globulin V. St, Protein standards; BSA, bovine serum albumin. B Tandem mass spectrometric identification of the 65 kDa protein (band b). Upper, the amino acid sequence of mouse serum albumin is shown. Red characters indicate the amino acid sequences determined by tandem mass spectrometric analysis. Lower, the product ion spectrum of the precursor fragment with 1149.65 of mass value obtained from band b. This spectrum identified the amino acid sequence LVQEVTDFAX, corresponding to amino acids 66–75 in mouse serum albumin. Amino acids Q, V and D, indicated by the product ion fragments, b7, y4, y6 and y8, are characteristic for mouse serum albumin but not for bovine or human albumin