Diffusion limited component of mitochondrial F1-ATPase.

1. The possibility that the rate of ATP hydrolysis by F1-ATPase approaches the diffusion-controlled limits was investigated by measuring the values of kcat and kl (kcat/Km) as a function of increasing viscosity. 2. The values of kcat/Km decrease significantly with increasing viscosity; further such decrease was lower when Fl-ATPase hydrolyzed poor substrate such as Ca- and Mg-ITP or when the hydrolysis rates were measured at temperatures below 20 degrees C. 3. Viscosity also decreases kcat, but only at high concentrations of viscosogenic agents. 4. These results suggest that ATP hydrolysis is at least partly diffusion-controlled, although a general nonspecific perturbation in the enzyme structure is also effected by viscosity.