Figure 3.

pH dependence of ATP hydrolysis by purified plasma membrane fractions prepared from YAKpma2, YAKpma4, Q882ochre, and T861N measured as described in Methods at the pH values indicated. ATPase activity is expressed as the percentage of maximal activity observed for each strain. The mean specific activities at the optimal pH were: 0.46 (PMA2), 0.60 (PMA4), 0.69 (T861N), and 1.01 (Q882ochre) μmol Pi min⁻¹ mg⁻¹.