Influence of Mg2+ and Ca2+ bound to 1,5‐IAEDANS‐labeled phosphorylated and dephosphorylated heavy meromyosin complexed with F‐actin on polarized fluorescence of the fluorophore

Dephosphorylated and phosphorylated heavy meromyosin, fluorescently labeled with 1,5‐IAEDANS attached at the SH1 group, was introduced into myosin‐free ghost fibres and the polarized fluorescence of the bound label was measured. The results depended on whether the divalent cation binding sites on heavy meromyosin were saturated with Mg2+ or Ca2+. The calculated angles of absorption and emission dipoles and the amount of random fluorophores were significantly changed, indicating that the random mobility and orientation of the fluorophores of phosphorylated and dephosphorylated heavy meromyosin heads complexed with F‐actin in the ghost fibre depend on saturation of heavy meromyosin with Ca2+ or Mg2+. The presence of bound Ca2+ has an opposite effect on the polarized fluorescence of phosphorylated and dephosphorylated 1,5‐IAEDANS‐heavy meromyosin.