Troponin C from Rabbit Slow Skeletal and Cardiac Muscle Is the Product of a Single Gene

Troponin C has been isolated from rabbit slow skeletal and cardiac muscle and the complete amino acid sequence of the slow muscle protein determined. Amino acid analysis and peptide mapping of the cardiac protein showed it to be very similar to, if not identical with, the slow muscle protein. This identity has been proved by the isolation and characterisation of tryptic peptides from the cardiac protein. It seems very likely that troponin C from these two tissues is the product of a single gene, in contrast to troponin I and troponin T which are the products of different genes. The amino acid sequences shows only one difference from that of bovine cardiac troponin C, the highly conservative replacement of an aspartic for a glutamic acid at position 115. No differences were found in the N-terminal region where these proteins appear to have a lost one of the Ca2+ binding sites found in fast skeletal muscle troponin C. The possible significance of this finding in relation to the binding of troponin C to the different types of troponin I is discussed.