THERMOPHILIC F1-ATPASE IS ACTIVATED WITHOUT DISSOCIATION OF AN ENDOGENOUS INHIBITOR, EPSILON SUBUNIT

Abstract Subunit complexes (α3β3γ, α3β3γδ, α3β3γe, and α3β3γδe) of thermophilic F1-ATPase were prepared, and their catalytic properties were compared to know the role of δ and e subunits in catalysis. The presence of δ subunit in the complexes had slight inhibitory effect on the ATPase activity. The effect of e subunit was more profound. The (−e) complexes, α3β3γ and α3β3γδ, initiated ATP hydrolysis without a lag. In contrast, the (+e) complexes, α3β3γe and α3β3γδe, started hydrolysis of ATP (<700 μm) with a lag phase that was gradually activated during catalytic turnover. As ATP concentration increased, the lag phase of the (+e) complexes became shorter, and it was not observed above 1 mm ATP. Analysis of binding and hydrolysis of the ATP analog, 2′,3′-O-(2,4,6-trinitrophenyl)-ATP, suggested that the (+e) complexes bound substrate only slowly. Differing fromEscherichia coli F1-ATPase, the activation of the (+e) complexes from the lag phase was not due to dissociation of e subunit since the re-isolated activated complex retained e subunit. This indicates that there are two alternative forms of the (+e) complex, inhibited form and activated form, and the inhibited one is converted to the activated one during catalytic turnover.