Comparison of the structure of two cardiac troponin T isoforms

Two isoforms of troponin T have been isolated from bovine cardiac muscle. One isoform has an M(r) of 31 000 and a pI about 7.1, the corresponding values for the second isoform being 33 000 and 6.5. Both isoforms have identical C- and N-terminal sequences, and, according to the data from tryptic-peptide mapping, a similar structure of the central and C-terminal domains. The large N-terminal peptides of troponin T isoforms differ in the content of glutamine/glutamic acid and alanine. It is concluded that the isoform with M(r) 33 000 has an additional peptide enriched with glutamic acid and alanine that is inserted between the N-terminal pentapeptide and the cysteine located 40-60 residues from the N-terminus.