Binding of phosphorylated and dephosphorylated heavy meromyosin to F-actin

The effect of myosin light chain phosphorylation in skeletal muscle was investigated with respect to the binding affinity of phosphorylated and dephosphorylated heavy meromyosin (HMM) for F-actin in the absence of ATP. For phosphorylated HMM the affinity was 2.5-times weaker in the presence of Ca2+ as in its absence (HMM divalent binding sites saturated only with Mg). For dephosphorylated HMM the reverse was true, the binding being 2.4-times higher in the presence of Ca2+.