FIG. 3.

Biochemical properties of the purified F₁F_o-ATPase. (A to E) Effects of temperature (A), extracellular pH (B), MgCl₂ (C), CaCl₂ (D), and ATP (E) on ATPase activity. (F) Stability of the purified enzyme (20 μg) (▴) in 10 mM Tris-Cl (pH 8.0) with 2 mM MgCl₂, compared to membrane vesicles (•) stored in membrane buffer at 4°C. ATPase activity was determined using the ATP-regenerating assay (B, E, and F) or by determination of P_i at 40°C (A, C, and D); 100% ATPase activity was in the range of 15 to 20 U/mg protein.