Fluorometric evidence for control of the activity of F1-adenosinetriphosphatase by ligand-induced conformation change.

The effect of ATP on the fluorescence intensity of bovine heart F1-adenosinetriphosphatase labeled at its essential Lys with 7-chloro-4-nitro-2,1,3-benzoxadiazole (N-NBD-F1) has been examined in solutions containing different concentrations of ADP. The fluorescence of N-NBD-F1 is unaffected by ATP in the absence of ADP. But when increasing amounts of ATP are added to a solution of N-NBD-F1 containing 0.37 or 1.0mM ADP, the fluorescence of N-NBD-F1 first decreases and then increases continually as the concentration of ATP is further raised. Parallel measurements of the suppression of the fluorescence of N-NBD-F1 and the inhibition of the ATPase activity of the unlabeled enzyme by ADP in the presence of ATP show a quantitative correlation between the changes in fluorescence and in ATPase activity. The data are consistent with the model for F1-ATPase with one principal catalytic beta' subunit for ATP hydrolysis and synthesis, and two auxiliary beta" subunits which control the conformation and hence the catalytic activity of beta' through interaction between all the subunits.