The effect of myosin regulatory eight chains on the aggregation of myosin active fragments

Aggregative characteristics (at 42 °C) of active skeletal muscle myosin fragments – chymotryptic subfragmenl 1 lacking regulatory light chain (RLC), Mg-papain subfragment 1, containing RLC, and heavy meromyosin, containing dephosphorylated or phosphorylated RLC – were studied comparatively. Besides hydrophobic interactions, divalent cations are shown to exert large influence on binding of RLC with myosin head hinge region. The experimental data suggest that in the presence of divalent cations RLC stabilizes the labile myosin head structures – 50 kDa fragment and «essential» light chain. The effect of RLC phosphorylation is opposite to divalent cation influence:it leads to some destabilization of head structure the evidence for which is the weaker binding of phosphorylated RLC to the head. It may be an inderect indication for «auxiliary» role of RLC phosphoryiation in functioning of skeletal muscle contractive system.