N-terminal amino acid sequences of troponin T fragments, including 30 kDa one, produced during postmortem aging of bovine longissimus muscle

We have determined the amino (N)-terminal amino acid (AA) sequences of five troponin T (TnT) fragments produced during postmortem aging of bovine longissimus muscle. Western blot analysis showed that 32.1, 28.8, 27, and 25.8 kDa anti-fast-type TnT (fTnT)-positive fragments and a 31 kDa anti-slow-type TnT (sTnT)-positive fragment were present at 14 d postmortem. The N-terminal AA sequences of the 32.1, 28.8 (conventional 30 kDa), 27, and 25.8 kDa fragments were APPPPAEV, EVHEPEEK, EKPRPRLT, and APKIPEGE, respectively, and they were mapped to the N-terminal region of bovine fTnT isoforms. The N-terminal sequences of the 31 kDa fragment, EAPEEPEP, were mapped to the sTnT isoforms. These findings indicate that the two isoform types of fTnT predominantly expressed in the longissimus muscle are cleaved specifically at Glu21–Ala22 and Glu15–Ala16, His37–Glu38 and His31–Glu32, Glu43–Glu44 and Glu37–Glu38, and/or Thr51–Ala52 and Thr45–Ala46, respectively, and that a sTnT isoform is cleaved specifically at Glu23–Glu24.