A 1 A O ATP synthases with a V-type c subunit have only been found in hyperthermophilic archaea which makes bioenergetic analyses impossible due to the instability of liposomes at high temperatures. A search for a potential archaeal A 1 A O ATP synthase with a V-type c subunit in a mesophilic organism revealed an A 1 A O ATP synthase cluster in the anaerobic, acetogenic bacterium Eubacterium limosum KIST612. The enzyme was purified to apparent homogeneity from cells grown on methanol to a specific activity of 1.2 UÁmg À1 with a yield of 12%. The enzyme contained subunits A, B, C, D, E, F, H, a, and c. Subunit c is predicted to be a typical V-type c subunit with only one ion (Na + )-binding site. Indeed, ATP hydrolysis was strictly Na + -dependent. N,N 0 -dicyclohexylcarbodiimide (DCCD) inhibited ATP hydrolysis, but inhibition was relieved by addition of Na + . Na + was shown directly to abolish binding of the fluorescence DCCD derivative, NCD-4, to subunit c, demonstrating a competition of Na + and DCCD/NCD-4 for a common binding site. After incorporation of the A 1 A O ATP synthase into liposomes, ATP-dependent primary transport of 22 Na + as well as DµNa + -driven ATP synthesis could be demonstrated. The Na + A 1 A O ATP synthase from E. limosum is the first ATP synthase with a V-type c subunit from a mesophilic organism. This will enable future bioenergetic analysis of these unique ATP synthases.
AbbreviationsDµNa + , electrochemical sodium ion potential; DpNa, sodium ion potential; DΨ, membrane potential; DCCD, N,N 0 -dicyclohexylcarbodiimide; DDM, n-dodecyl-b-maltoside; ETH 2120, N,N,N,N 0 -tetra-cyclo-hexyl-1,2-phenylenedioxydiacetamide; MALDI, matrix-assisted laser desorption/ ionization; TCS, 3,3 0 ,4 0 ,5-tetrachlorosalicylanilide.