Heterogeneity of 27,000 dalton-light chain of cardiac ventricular myosin.

Electrophoretic analysis on sodium pyrophosphate gels of myosin light chain 1 (LC-1; 27,000 daltons) from rabbit ventricular heart muscle revealed the presence of two distinct components named LC-1a (10%) and LC-1b (90%). After thyroxine administration, a shift toward LC-1a (45%) was observed. Canine cardiac ventricular light chain 1 (27,000 daltons) had equal amounts of LC-1a' (50%) and LC-1b' (50%), which corresponded to LC-1a and LC-1b of rabbit heart, respectively. However, heterogeneity of light chain 2 (20,000 daltons) was not observed. It is concluded that cardiac ventricular myosin has two heterogeneous 27,000 dalton-light chains and that the proportion of these proteins varies according to the thyroid status and animal species.