title: Kinetic model for the interaction of myosin subfragment 1 with regulated actin.
abstract: A one-dimensional kinetic Ising model is developed to describe the binding of myosin subfragment 1 (SF-1) to regulated actin. The model allows for cooperative interactions between individual actin sites with bound SF-1 ligands rather than assuming that groups of actin monomer sites change their state in a cooperative fashion. With the triplet closure approximation, the model yields a set of 16 independent differential (master) equations which may be solved numerically to yield the extent of binding as a function of time. The predictions of the model are compared with experiments on the transient binding of SF-1 to regulated actin in the presence of Ca2+ and in the absence of Ca2+ with varying amounts of SF-1 prebound to the actin filament and on the equilibrium binding of SF-1 X ADP to regulated actin in the absence of Ca2+. In all cases, the calculations fit the data to within the experimental errors. In the case of SF-1 X ADP, the results suggest that a repulsive interaction exists between adjacently bound SF-1 at the ends of two neighboring seven-site actin units.
mesh_terms: D000199:Actins; D007700:Kinetics; D008956:Models, Chemical; D015879:Myosin Subfragments; D009218:Myosins; D010446:Peptide Fragments; D011485:Protein Binding
chemical_list: D000199:Actins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D009218:Myosins