The amino acid sequence of rabbit slow-muscle troponin I.

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Abstract
Troponin I was isolated from 6 red muscles in the hind leg of the rabbit. Soleus, semitendinosus, vastus intermedius and adductor longus muscles contained primarily slow-muscle troponin I, vastus lateralis contained fast-muscle troponin I and quadratus femoris contained a mixture of the 2. The complete amino acid sequence of the troponin I from slow muscle was determined. Seven CNBr [cyanogen bromide] fragments were isolated and sequenced by using the dansyl-Edman technique after digestion with proteolytic enzymes. The CNBr fragments were ordered by isolation of tryptic peptides containing carboxy[14C]methylmethionine. Direct evidence for the conjunction of residues 8 and 9 was not obtained and 1 of the carboxyl groups between residues 71 and 79 may carry an amide group. Slow-muscle troponin I was a single polypeptide chain of 184 residues with a MW of 21,146. It had a net overall positive charge of 18 at pH 7 and an absorption coefficient, of 5.43. The protein was isolated with both a blocked and an unblocked N-terminus, although the nature of the blocking group was not determined. Proline was the N-terminal amino acid. Two forms of the protein were also distinguished by the presence of an extra 2 residues at the C-terminus. Comparison of sequences of troponin I from rabbit slow, fast and cardiac muscle showed that homology was most marked in the C-terminal half of the molecules. Towards the N-terminus the homology became much less marked.