Effect of a panel of standard inhibitors and polygodial
against membrane-bound ATPases in S. cerevisiae at pH
5.7 (filled bars) and pH 8.5 (open bars). Whole membranes were used,
and the amount of enzyme activity ranged from 0.7 to 1.1 U (nanomoles
of Pi per minute), with specific activity ranging from 50
to 90 U/mg. The inhibition ratio (percentage) was calculated as
follows: {1 − [(I − C2)/(C1
− C2)] × 100}, where C1 is enzyme alone,
I is enzyme plus inhibitor, and C2 is inhibitor
without enzyme (10 mM ATP present in all). Inhibitors were used at
concentrations known to give maximal inhibition of their selective
enzyme. KN3, potassium azide at 5 mM; VO4, sodium orthovanadate at 100
μM; Baf, bafilomycin at 50 nM; AM, ammonium molybdate at 0.2 mM;
Polyg, polygodial at 50 μg/ml. Values are means ± standard
deviations.