Studies on Ca²⁺-Mg²⁺ Binding Sites of Frog Skeletal Muscle Myosin

Abstract

Frog skeletal muscle myosin light chains readily dissociate from the myosin oligomer in the absence of divalent cations, and unlike rabbit skeletal muscle myosin light chains, the released light chains of frog skeletal muscle myosin have a high Ca²⁺ binding affinity. Whereas each Ca²⁺ binding light chain of frog skeletal muscle myosin, when in association with the heavy chains bound 1 mol of Ca²⁺, when in the dissociated state bound 0.5 mol of Ca²⁺; the latter were readily displaced with low Mg²⁺ concentrations. Whereas 10^-5M Mg²⁺ displaced all of the Ca²⁺ biding sites on the released light chains at Ca²⁺ concentration ranges of 10^-7 to 10^-4M, there was negligible displacement of the Ca²⁺ binding sites with native frog skeletal muscle myosin under these same conditions.