Electrophoretic Mobility of Cardiac Myosin Heavy Chain Isoforms Revisited: Application of MALDI TOF/TOF Analysis

The expression of two cardiac myosin heavy chain (MyHC) isoforms in response to the thyroid status was studied in left ventricles (LVs) of Lewis rats. Major MyHC isoform in euthyroid and hyperthyroid LVs had a higher mobility on SDS-PAGE, whereas hypothyroid LVs predominantly contained a MyHC isoform with a lower mobility corresponding to that of the control soleus muscle. By comparing the MyHC profiles obtained under altered thyroid states together with the control soleus, we concluded that MyHC alpha was represented by the lower band with higher mobility and MyHC beta by the upper band. The identity of these two bands in SDS-PAGE gels was confirmed by western blot and mass spectrometry. Thus, in contrast to the literature data, we found that the MyHC alpha possessed a higher mobility rate than the MyHC beta isoform. Our data highlighted the importance of the careful identification of the MyHC alpha and MyHC beta isoforms analyzed by the SDS-PAGE.