Difference in postmortem degradation pattern among troponin T isoforms expressed in bovine longissimus, diaphragm, and masseter muscles

The postmortem degradation of troponin T (TnT) in bovine longissimus (LT), diaphragm (DP), and masseter (MS) was analyzed. A 28.3 kDa (conventional 30 kDa) fragment of fast-type TnT isoforms showed the highest content in both LT and DP, where a 35.4 kDa isoform had the highest expression among the other fast isoforms. Meanwhile, a 26.0 kDa fragment was found to be the most highly produced among the fast TnT fragments in MS, where the expression of 36.5 and 32.8 kDa isoforms was higher than that of 35.4 and 34.8 kDa isoforms. Thus, the compositions of both the intact TnT isoform proteins and the postmortem fragments differed among the muscles examined, indicating that each TnT isoform degrades into a specific fragment in each muscle. Among the muscles, the LT muscle showed a high extent of TnT degradation and the highest expression of fast TnT isoforms containing a taste-related peptide sequence.