The effect of cross-innervation on the tropomyosin composition of rabbit skeletal muscle.

Soleus, semitendinosus and crureus muscles of the rabbit were found to contain alpha- and beta-tropomyosin subunits and additional forms that have been provisionally designated gamma and delta. Extensor digitorum longus and psoas muscles contained only alpha and beta subunits, the relative proportions of which varied between single fibres of psoas muscle. On cross-innervation of rabbit soleus and extensor digitorum longus muscles, the fraction of the total tropomyosin present as the beta subunit remained constant. The relative proportions of alpha, gamma and delta subunits changed as would be expected from the change in speed that occurred.