Fe(III) Binding to Bacillus PS3 F1ATPase, αβ Subcomplexes and Isolated α- and β-Subunits

Abstract

Isolated α- and β-subunits of Thermophilic Bacillus PS3 F1ATPase (TF1) bind about 1 Fe(III) equivalent. Upon reassembling in the symmetric α3β3 hexamer, Fe(III) binding capacity decreases, as this complex binds about three Fe(III) equivalents. In accordance, when the hexamer is dissociated in the α1β1 heterodimer, each heterodimer binds about one Fe(III) equivalent. On the contrary, native TF1 exhibits a single Fe(III) site. CD spectra in far UV indicate that upon Fe(III) binding both the whole complex and the isolated β-subunit undergo structural modifications accompanied by decrease of α-helix content, while α-subunit doesn't. As in α3β3 and in the whole enzyme the number of bound Fe(III) equivalents is consistent with the number of β-subunits in the “empty” conformation, it is inferred that the single Fe(III) site in TF1 is probably located in βE.