Cation requirement for the reconstitution of oligomycin-sensitive ATPase by means of soluble F 1-ATPase and F 1-depleted submitochondrial particles

Abstract

Bovine heart submitochondrial particles depleted of F 1 by treatment with urea (‘F 1-depleted particles’) were incubated with soluble F 1-ATPase. The binding of F 1 to the particles and the concomitant conferral of oligomycin sensitivity on the ATPase activity required the presence of cations in the incubation medium. NH + 4, K +, Rb +, Cs +, Na + and Li + promoted reconstitution maximally at 40–74 mM, guanidinium + and Tris + at 20–30 mM, and Ca 2+ and Mg 2+ at 3–5 mM. The particles exhibited a negative ζ-potential, as determined by microelectrophoresis, and this was neutralized by mono- and divalent cations in the same concentration range as that needed to promote F 1 binding and reconstitution of oligomycin-sensitive ATPase. It is concluded that the cations act by neutralizing negative charges on the membrane surface, mainly negatively charged phospholipids. These results are discussed in relation to earlier findings reported in the literature with F 1-depleted thylakoid membranes and with submitochondrial particles depleted of both F 1 and the coupling proteins F 6 and oligomycin sensitivity-conferring protein.