A Highly Stable Adenosine Triphosphatase from a Thermophilic Bacterium

1. A highly stable ATPase (TF,) was purified to a monodispersed state from the membranes of a thermophilic bacterium PS3. Its molecular weight was 380,000, and it was composed of five subunits cy, p, y, a’, and 6 with molecular weights of 56,000, 53,000, 32,000, 15,500, and 11,000, respectively. 2. TF, was stable against dissociating agents such as 5.5 M urea and 4.0 M LiCl, organic solvents, such as 60% acetone, heavy metals, and detergents. Low concentrations of all these agents stimulated its activity at 60”. 3. TF, was not cold-labile and showed maximal activity at 70”. Its CD spectrum revealed that its conformation changed between 81 and 96”, and that its contents of LY helices and p structures were 27.3 and 12.8%, respectively, at 75”. 4. TF, was completely dissociated by treatment with dodecyl sulfate at 60” and then with 7.1 M urea. The dissociated TF 1 was reconstituted by treatment with Dowex l-X2, and then dialysis. 5. [3H]Acetyl-TF, bound to TF,-depleted membranes. TF, only catalyzed ‘*P,-ATP exchange and showed sensitivity to inhibitors of energy transfer when bound to the membranes. 6. A hydrophobic membrane component (TF,) was isolated which rendered TF, sensitive to inhibitors of energy transfer. It was composed of three subunits (with molecular weights of 19,000, 13,500, and 5,400) and P-lipids.