A protein friction model of the actin sliding movement generated by myosinin mixtures of MgATP and MgGTP in vitro

The sliding movement of an actin filament generated by myosin heads with Mg GTP bound is much slower than that by those with MgATP bound. Nonetheless, there is a report that the actin sliding velocity at low (11-21 mu M) MgHTP concentrations is increased by the addition of MgGTP in a range of 1-3 mM, although the actin sliding velocity at these MgATP concentrations is large r than the maximum sliding velocity attained in the presence of MgGTP alone . The convex rise in the velocity was called "mutual sensitization of MgATP and MgGTP" in the report. Here we propose a theoretical model to account f or the mutual sensitization of MgATP and MgGTP. The model is an extension o f a protein friction model, accommodating the presence of two different sub strates and assuming the presence of motile and non-motile myosins. This ne w model is in accord with the characteristics of the actin/myosin sliding m ovement experimentally observed in mixtures of MgATP and MgGTP. Comparison of the model with the experimental results implies that the non-motile and motile myosins are those with the "converse and correct" orientations of th eir heads with respect to the direction of the actin sliding movement in vi tro. (C) 1999 Academic Press.