Effect of phosphorylation of rabbit skeletal muscle myosin light chains on the nature of conformational changes of F-actin induced by heavy meromyosin

The changes in F-actin conformation in myosin-free single ghost fiber induced by the binding of heavy meromyosin (HMM) with dephosphorylated or phosphorylated light chains-2 (LC₂) have been studied by measuring intrinsic tryptophan polarized fluorescence of F-actin. It has been found that at low concentrations of Ca²⁺ (pCa ≥ 8), the binding of HMM with dephosphorylated LC₂ to F-actin in ghost fibres increases, whereas the binding of HMM with phosphorylated LC₂ decreases the anisotropy of polarized tryptophan fluorescence. The effect is reversed at high concentrations of Ca²⁺ (pCa = 5). It has been assumed that this effect of myosin light chain phosphorylation may be due to its influence on the type of myosin head binding to F-actin.