Myosin isoforms and myofibrillar protein phosphorylation. A. Gel electrophoresis stained with Coomassie-Blue demonstrate 100% β-MyHC content in both HG and nonHG groups due to hypothyroidism. In euthyroid rats, HG results in a significant upregulation of cardiac β-MyHC compared to the α-MyHC predominately expressed in the nonHG rat heart. B and C. Coomassie-blue and phospho-stain by Pro-Q Diamond indicated similar phosphorylation profiles of myofibrillar proteins in HG and nonHG. D. Western blots of phosphorylated MLC2 (MLC2-P) and total MLC content demonstrated similar degrees of phosphorylation in HG and nonHG controls. Additional lanes indicating alkaline phosphatase (AP) treatment to dephosphorylate MLC2 and myosin light chain kinase (MLCK) treatment to phosphorylate MLC2 provided negative and positive controls for MLC2 phosphorylation. Myosin = chicken skeletal myosin standard, Tn = bovine cardiac troponin standard, MyBP-C = myosin binding protein-C, Tm = tropomyosin, LC = myosin light chain.