The effects of solvent viscosity on the kinetic parameters of myosin and heavy meromyosin ATPase.

The effects of different solvent viscosities on the kinetic parameters of ATP hydrolysis by myosin and heavy meromyosin (HMM) were investigated at high and low ionic strength (i.e., 0.53 and 0.08 M KCl where myosin is polymerized into thick filament). The solvent viscosity was adjusted by the addition of appropriate amounts of sucrose. The maximum rate constants (Vm) for both myosin and HMM decreased monotonically with increasing solvent viscosity at either ionic strength. The Michaelis constants (Km) for soluble myosin and HMM became minima at a viscosity nearly twice that of the solvent without sucrose, then increased abruptly with increasing solvent viscosity. On the other hand, Km of polymerized myosin at the low ionic strength decreased monotonically with increasing solvent viscosity. These experimental results are discussed with special reference to Kramers' kinetic theory of a chemically reacting system in viscous media.