Coupling factor 1 from Escherichia coli lacking subunits .delta. and .epsilon.: preparation and specific binding to depleted membranes, mediated by subunits .delta. or .epsilon.

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Abstract
A procedure for the preparation of coupling factor 1 (F1) from Escherichia coli lacking subunits .delta. and .epsilon. is described. Using chloroform and dimethyl sulfoxide, we can isolate F1 containing only subunits .alpha., .beta. and .gamma. [F1(.alpha..beta..gamma.)] directly from membrane vesicles in 10-mg quantities. Pure and active subunits .delta. and .epsilon. were prepared from five-subunit F1 by sodium dodecyl sulfate-polycarylamide gel electrophoresis. After addition of these subunits, F1(.alpha..beta..gamma.) is as active in reconstituting ATP-dependent transhydrogenase as five-subunit F1. The ATPase activity of F1(.alpha..beta..gamma.) is inhibited by subunit .epsilon. in a 1:1 stoichiometry to the same extent (.apprxeq.90%) and with the same affinity (Ki = 0.2-0.8 nM) as reported earlier [Dunn, S. D. (1982) J. Biol. Chem. 257, 7354-7359]. In the presence of either .delta. or .epsilon., F1(.alpha..beta..gamma.) binds to F1-depleted membrane vesicles and to liposomes containing the membrane sector (Fo) of the ATP synthase to an extent commensurate with the Fo content. The binding ratios .epsilon./F1(.alpha..beta..gamma.) and probably also .delta./F1(.alpha..beta..gamma.) are close to unity. The specific, .delta.- or .epsilon.-deficient F1.cntdot.Fo complexes presumably formed show ATPase activities sensitive to subunit .epsilon. but not to dicyclohexylcarbodiimide, and no energy-transfer capabilities. Binding studies at different pH values suggest that F1-Fo interactions in the presence of both subunits .delta. and .epsilon. are similar to a combination of those mediated by .delta. or .epsilon. alone. Salts containing mono-, di- or trivalent cations promote specific binding of F1(.alpha., .beta., .gamma.) by .delta. or .epsilon. at concentrations of about 0.1, 0.001, and 0.01 M, respectively, suggesting a general electrostatic effect.