Abstract
The epsilon subunit of F(1)-ATPase from the thermophilic Bacillus PS3 (TF(1)) has been shown to bind ATP. The precise nature of the regulatory role of ATP binding to the epsilon subunit remains to be determined. To address this question, 11 mutants of the epsilon subunit were prepared, in which one of the basic or acidic residues was substituted with alanine. ATP binding to these mutants was tested by gel-filtration chromatography. Among them, four mutants that showed no ATP binding were selected and reconstituted with the alpha(3)beta(3)gamma complex of TF(1). The ATPase activity of the resulting alpha(3)beta(3)gammaepsilon complexes was measured, and the extent of inhibition by the mutant epsilon subunits was compared in each case. With one exception, weaker binding of ATP correlated with greater inhibition of ATPase activity. These results clearly indicate that ATP binding to the epsilon subunit plays a regulatory role and that ATP binding may stabilize the ATPase-active form of TF(1) by fixing the epsilon subunit into the folded conformation.
Highlights
The ⑀ subunit of F1-ATPase from the thermophilic Bacillus PS3 (TF1) has been shown to bind ATP
These results clearly indicate that ATP binding to the ⑀ subunit plays a regulatory role and that ATP binding may stabilize the ATPase-active form of TF1 by fixing the ⑀ subunit into the folded conformation
As the smallest subunit of F1-ATPase, the ⑀ subunit acts as an endogenous inhibitor of the ATPase activity in both the bacterial and chloroplast F1-ATPase, where it is believed to play a regulatory role in ATP synthase [7,8,9,10]
Summary
The ⑀ subunit of F1-ATPase from the thermophilic Bacillus PS3 (TF1) has been shown to bind ATP. The ATPase activity of the resulting ␣33␥⑀ complexes was measured, and the extent of inhibition by the mutant ⑀ subunits was compared in each case. These results clearly indicate that ATP binding to the ⑀ subunit plays a regulatory role and that ATP binding may stabilize the ATPase-active form of TF1 by fixing the ⑀ subunit into the folded conformation.
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