Influence of salt and pyrophosphate on bovine fast and slow myosin S1 dissociation from actin

The kinetics of myosin dissociation from actin was investigated and also the impact of salt, MgPPi, and myosin heavy chain isoform on myosin subfragment 1 (S1) dissociation from actin using purified proteins and fluorescence spectroscopy. Both NaCl and MgPPi increased myosin S1 dissociation rate. When salt concentrations increased from 0.1 to 1.0 M, the dissociation rate of S1 from bovine masseter (slow) and cutaneous trunci (fast) muscle increased 38 and 78-fold, respectively. MgPPi had an even greater effect on S1 dissociation from actin. With the addition of MgPPi to the mixture of pyrene actin and S1, the fluorescence increased about 85% within the dead time of the mixing approach. Unlike salt, MgPPi had no apparent difference in its ability to dissociate slow or fast S1 isoforms from actin. The results reveal that salt and MgPPi increase myosin extraction and functionality in meat by weakening the actomyosin interaction and that some of the difference in the functionality of red and white muscle may be related to actomyosin dissociation.