Molecular mechanism of Energy conversion on the biomembrane

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In order to know how many functional catalytic sites are necessary for ATPase activity of F1-ATPase from a thermophilic Bacillus PS3, a new method to isolate homogeneous prepartion of the alpha3beta3gamma complex with 1,2, or 3 incompetent catalytic sites was developed. Ten glutamic acids (Glu・Tag) were linked to C-terminus of the catalytically incompetent beta (E190Q) subunit. Glu・Tag itself did not affect ATPase activity of the complexes. Two kinds of alpha3beta3gamma complexes, one containing beta (wild-type) and the other Glu・Tag-linked beta (E190Q), were mixed, urea-denatured, dialyzed, and alpha3beta3gamma complexes were reconstituted. Each of the complexes containing different number of Glu・Tag-linked beta (E190Q) was separated by anion-exchange chromatography and analyzed. The results were as follows. 1) Normal steady-state ATPase activity requires three intact catalytic sites. 2) Chase-acceleration, a catalytic cooperativity, requires at least two intact catalytic sites. 3) Single-site catalysis can be mediated by a single intact catalytic site alone. Re-scrambling of subunits between complexes could occur when the complex was aged under some condition and this might be one of the reasons of the previous contradictory result (Miwa et al. (1989) J.Biochem. (Tokyo) 106,730-734).