(A and B) Effect of increasing yeast plasma membrane H+-ATPase activity by switching from N2 to O2 (dashed line) at t = 0. (Arrows) At −2 min, either DMSO alone (control) or a DMSO solution of ebselen (2-phenyl-1,2-benzisoselenazol-3(2H), an H+-ATPase inhibitor) was added to the suspension. Mean (± SD); (asterisk) p < 0.05 ebselen versus control. (A) τi−1 for control (□, n = 4) and ebselen-treated (■, n = 5) suspensions. (B) HPLC ATP measurements plotted from separate studies of control (□, n = 4) and ebselen-treated (■, n = 4) suspensions. (C) τi−1 for (□) control, (■) ebselen-treated, and (♦) PMA1+/− yeast suspensions in the N2 (4 min before O2) and O2 conditions (6 min after N2). τi−1 for control yeast suspensions increased going from N2 to O2 (p < 0.001), whereas the ebselen-treated and PMA1+/− yeast τi−1 values were unchanged. Control and ebselen-treated τi−1 are from panel A. The individual measurement values as well as the mean (dashed) and SD (solid) horizontal lines are shown. (Pound sign) p < 0.05 O2 versus N2 same group.