The Ionic Track in the F1-ATPase from the Thermophilic Bacillus PS3†

Only β−β cross-links form when the α3(βE395C)3γK36C (MF1 residue numbers) double mutant subcomplex of TF1, the F1-ATPase from the thermophilic Bacillus PS3, is slowly inactivated with CuCl2 in the presence or absence of MgATP. The same slow rate of inactivation and extent of β−β cross-linking occur upon treatment of the α3(βE395C)3γ single mutant subcomplex with CuCl2 under the same conditions. In contrast, the α3(βE395C)3γR33C and α3(βE395C)3γR75C double mutant subcomplexes of TF1 are rapidly inactivated by CuCl2 under the same conditions that is accompanied by complete β−γ cross-linking. The ATPase activity of each mutant enzyme containing the βE395C substitution is stimulated to a much greater extent by the nonionic detergent lauryldimethylamine oxide (LDAO) than wild-type enzyme, whereas the ATPase activities of the γR33C, γK36C, and γR75C single mutants are stimulated to about the same extent as wild-type enzyme by LDAO. This indicates that the E395C substitution in the 394DELSEED400 segment of β sub...