Comparison of superprecipitation and contractile protein contents of myosin B in the myocardium and conduction system.

The extents of superprecipitation and contractile protein contents of myosin B in the myocardium and conduction system were compared. The extents of superprecipitation of myosin B of the two types of cardiac muscle were similar, but the onset of the superprecipitation reaction of myosin B from the conduction system was delayed and the clearing phase of the reaction was prolonged. On sodium dodecyl sulfate (SDS)-polyacrylamide gel (6%) electrophoresis of myosin B, myosin, actin, and tropomyosin were clearly separated. The amounts of protein present in stained bands of polyacrylamide gels were estimated. The weight ratios of myosin: actin, tropomyosin: myosin, and actin: tropomyosin in myosin B were not significantly different in the two types of cardiac muscle. However, the compositions of myosin light chains in the two types of cardiac muscle were quite different. It was suggested that this difference of myosin subunits might contribute to the difference in superprecipitation of myosin B.