Purified preparations of rabbit skeletal white, red, and cardiac muscle myosin (WM, RM, and CM) were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Significant differences in both the molecular weights and number of light chains in these myosins were found. WM has three distinct light-chain components (LCiw, LC2W, LC3W) having molecular weights of 25,500, 17,400, and 15,100, respectively (29), extensively used for the separation of various proteins and the determination of their molecular weights, we decided to apply this method to a reinvestigation of the light chains of rabbit WM, RM, and CM. Our results clearly show that both quantitative and qualitative differences exist between light chains in the different types of muscle; these will be discussed in terms of the isozymic nature of myosin.
MATERIALS AND METHODS Preparation of myosinRabbit soleus, semitendinosus, crureus, and intertransversarius (red muscles); the outer layers of vastus lateralis and adductor magnus (white muscles); and heart ventricle (cardiac muscle) were used for the preparation of myosin (8). Myosin was further purified by column chromatography on DEAE-Sephadex A-50, essentially by the methods of Richards et al. (30). 150-200 mg of myosin, dissolved in a solution containing 0.04 M Na4P207 (pH 7.5), 0.1 mM EDTA, and 0.1 mM dithiothreitol (buffer I), were applied to a column (2.5 X 35 cm) of DEAE-Sephadex A-50 equilibrated with the same buffer. The column was then washed with 2-3 column volumes of buffer I. Under these conditions myosin remained on the column, but other proteins (5-10% of the input) were eluted. A linear gradient of 0-0.5 AI NaCl in buffer I was then applied. Myosin was eluted as a sharp single peak at 0.13-0.15 M NaCl and concentrated by precipitation either at low ionic strength after dilution or with (NH4)2SO4 at 50% saturation. Myosin was finally dissolved in a solution containing 0.01 M sodium phosphate (pH 7.0), 0.5 M NaCl, 0.1 mM EDTA, and 0.1 mM dithiothreitol (buffer II). For the determination of ATPase activities of column-purified myosin, K4P207 and KCl were used in the elution buffers for chromatography and myosin was finally dissolved in a solution containing 0.5 M KCl, 1 mM EDTA, and 10 mM Ntris(hydroxymethyl) methyl-2-aminoethane sulfonic acid (TES), pH 7.0.Typical