Key result
Conduction system myosin B delays and prolongs superprecipitation versus myocardium, driven by light chain differences.
Why the study?
Differences in superprecipitation and contractile protein contents of myosin B between myocardium and conduction system were not fully characterized.
Distinct conduction system myosin properties warrant no clinical change; leaves open isoform-specific studies in arrhythmogenesis.
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.
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Saito et al. (1982) studied this question. Myosin B from conduction system vs. Myosin B from myocardium was evaluated on Superprecipitation and contractile protein ratios. Myosin B from the cardiac conduction system showed delayed onset and prolonged clearing phase of superprecipitation compared to myocardium, likely due to differences in myosin light chain composition.
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