Inhibition by trifluoperazine of ATP synthesis and hydrolysis by particulate and soluble mitochondrial F1: competition with H2PO4-.

The effect of trifluoperazine (TFP) on the ATPase activity of soluble and particulate F1-ATPase and on ATP synthesis driven by succinate oxidation in submitochondrial particles from bovine heart was studied at pH 7.4 and 8.8. At the two pH, TFP inhibited ATP hydrolysis. Inorganic phosphate protected against the inhibiting action of TFP. The results on the effect of various concentrations of phosphate in the reversal of the action of TFP on hydrolysis at pH 7.4 and 8.8 showed that H2PO4- is the species that competes with TFP. The effect of TFP on oxidative phosphorylation was studied at concentrations that do not produce uncoupling or affect the aerobic oxidation of succinate (< 15 microM). TFP inhibited oxidative phosphorylation to a higher extent at pH 8.8 than at pH 7.4; this was through a diminution in the Vmax, and an increase in the Km for phosphate. Data on phosphate uptake during oxidative phosphorylation at several pH showed that H2PO4- is the true substrate for oxidative phosphorylation. Thus, in both synthesis and hydrolysis of ATP, TFP and H2PO4- interact with a common site. However, there is a difference in the sensitivity to TFP of ATP synthesis and hydrolysis; this is more noticeable at pH 8.8, i.e., ATPase activity of soluble F1 remains at about 40% of the activity of the control in a concentration range of TFP of 40-100 microM, whereas in oxidative phosphorylation 14 microM TFP produces a 60% inhibition of phosphate uptake.