Lobster troponin C: amino acid sequences of three isoforms.

We have determined the amino acid sequences of the three major isoforms of lobster troponin C, using protein chemistry methods. Each isoform contains 150 amino acid residues, with a calculated Mr of 17,000 +/- 100. Sequence differences occur in all regions of the polypeptides, indicating that the isoforms are products of three different genes, rather than alternative transcripts of a single gene. Analysis of the sequences predicts that functional Ca(2+)-binding sites are present only in regions II and IV of four ancestral regions.