Dimerization of the polypeptide chains of skeletal muscle tropomyosin

The composition of alpha and beta chains in tropomyosin dimers present in fetal and adult skeletal muscle of cow has been analysed by SDS-polyacrylamide gel electrophoresis after cross-linking of the chains by disulphide bridges. The results indicate that in vivo alpha beta heterodimers of tropomyosin are assembled preferentially and only the excess of particular chains forms homodimers, i.e., alpha alpha dimers in adult and beta beta ones in fetal muscle. The original dimers of tropomyosin were dissociated with urea in the presence of dithiothreitol. Subsequent reassembly of the tropomyosin dimers from the mixture of alpha and beta chains approaches the random model.