Postmortem changes in bovine troponin T isoforms on two-dimensional electrophoretic gel analyzed using mass spectrometry and western blotting: The limited fragmentation into basic polypeptides

To comprehend postmortem changes in troponin T (TnT), whole beef proteins were developed on a two-dimensional electrophoretic gel. Multiple TnT-related spots were identified by both western blotting and MALDI-TOF MS utilizing bovine TnT isoform mRNA sequences. More than 10 TnT fast-type isoform spots (pI 5.7–9.6<) and the two slow-type isoform spots (pI 5.6–5.7) were observed at slaughter. All the isoforms were degraded exclusively into basic spots (pI 9.6<) at day 14 postmortem. Some TnT-related phosphorylated spots present at slaughter had disappeared by day 14, suggesting that the phosphorylated N-terminal region was cut off during beef aging. The intact isoforms and the fragments were identified by the MS with sequence coverage of 20.8–62.7%, and two of the fragments included the cutting site peptide of a conventional 30 kDa or of a slow TnT-derived fragment. These results revealed that all of the TnT isoforms are cut exclusively in the glutamic acid-rich amino-terminal region during postmortem aging.