Binding of divalent cations by canine cardiac myosin: differences in normal right and left ventricles dependent upon number of light chains.

The moles of calcium bound by the left ventricle were 1.5 +/- 0.1, while those of the right ventricle were 2.9 +/- 0.2. The calcium binding constants were the same between myosins of the two cardiac ventricles. The Ca2+ binding constants were approximately 1.1 X 10(5) M-1 for both left and right ventricular myosins. Left ventricular myosin bound 1.3 +/- 0.1 mol of Mn2+, whereas right ventricular myosin bound 2.8 +/- 0.1 mol of Mn2+. The divalent cation Mn2+ only partially competed out Ca2+ (50%). Because of the partial competition, it seemed that Ca2+ and Mn2+ had some sights in common. These studies demonstrate a twofold difference in divalent cation binding (Ca2+, Mn2+) between left and right ventricular myosins. This variation in cation binding between the two ventricles is reflected in similar differences in myosin ATPase activity between the two ventricles.