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 k(cat) and k1 (k(cat)/K(m)) as a function of increasing viscosity. 2. The values of k(cat)/K(m) decrease significantly with increasing viscosity; further such decrease was lower when F1-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 k(cat), but only at high concentrations of viscosogenic agents. 4. These results suggest that ATP hydrolysis is at least partly diffusion-controlled, although a general non-specific perturbation in the enzyme structure is also effected by viscosity.