DIFFUSION-LIMITED COMPONENT OF MITOCHONDRIAL F1-ATPASE

1. The possibility that the rate of ATP hydrolysis by F1-ATPase approa ches the diffusion-controlled limits was investigated by measuring the values of k(cat) and k1 (k(cat)/K(m)) as a function of increasing vis cosity. 2. The values of k(cat)/K(m) decrease significantly with incre asing viscosity; further such decrease was lower when F1-ATPase hydrol yzed poor substrate such as Ca- and Mg-ITP or when the hydrolysis rate s were measured at temperatures below 20-degrees-C. 3. Viscosity also decreases k(cat), but only at high concentrations of viscosogenic agen ts. 4. These results suggest that ATP hydrolysis is at least partly di ffusion-controlled, although a general non-specific perturbation in th e enzyme structure is also effected by viscosity.