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J Biol Chem, Vol. 275, Issue 2, 906-912, January 14, 2000

Hybrid Rhodospirillum rubrum F₀F₁ ATP Synthases Containing Spinach Chloroplast F₁  or  and  Subunits Reveal the Essential Role of the  Subunit in ATP Synthesis and Tentoxin Sensitivity^*

Ward C. Tucker^§¶, Ziyun Du, Ray Hein^§, Mark L. Richter^§, and Zippora Gromet-Elhanan

From the  Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel and the ^§ Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas 66045

Trace amounts (~5%) of the chloroplast  subunit were found to be absolutely required for effective restoration of catalytic function to LiCl-treated chromatophores of Rhodospirillum rubrum with the chloroplast  subunit (Avital, S., and Gromet-Elhanan, Z. (1991) J. Biol. Chem. 266, 7067-7072). To clarify the role of the  subunit in the rebinding of , restoration of catalytic function, and conferral of sensitivity to the chloroplast-specific inhibitor tentoxin, LiCl-treated chromatophores were analyzed by immunoblotting before and after reconstitution with mixtures of R. rubrum and chloroplast  and  subunits. The treated chromatophores were found to have lost, in addition to most of their  subunits, approximately a third of the  subunits, and restoration of catalytic activity required rebinding of both subunits. The hybrid reconstituted with the R. rubrum  and chloroplast  subunits was active in ATP synthesis as well as hydrolysis, and both activities were completely resistant to tentoxin. In contrast, a hybrid reconstituted with both chloroplast  and  subunits restored only a MgATPase activity, which was fully inhibited by tentoxin. These results indicate that all three copies of the R. rubrum  subunit are required for proton-coupled ATP synthesis, whereas for conferral of tentoxin sensitivity at least one copy of the chloroplast  subunit is required together with the chloroplast  subunit. The hybrid system was further used to examine the effects of amino acid substitution at position 83 of the  subunit on sensitivity to tentoxin.

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