Fe(III) binding to Bacillus PS3F(1)ATPase, alpha beta subcomplexes and isolated alpha- and beta-subunits

Isolated alpha- and beta -subunits of Thermophilic Bacillus PS3 F(1)ATPase (TF1) bind about 1 Fe(III) equivalent. Upon reassembling in the symmetric a lpha (3)beta (3) hexamer, Fe(III) binding capacity decreases, as this compl ex binds about three Fe(III) equivalents. In accordance, when the hexamer i s dissociated in the alpha (3)beta (3), heterodimer, each heterodimer binds about one Fe(III) equivalent. On the contrary, native TF1 exhibits a singl e Fe(III) site. CD spectra in far UV indicate that upon Fe(III) binding bot h the whole complex and the isolated beta -subunit undergo structural modif ications accompanied by decrease of alpha -helix content, while cu-subunit doesn't. As in alpha (3)beta (3), and in the whole enzyme the number of bou nd Fe(III) equivalents is consistent with the number of beta -subunits in t he "empty" conformation, it is inferred that the single Fe(III) site in TF1 is probably located in beta (E). (C) 2001 Academic Press.