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 F-1-ATPase and on ATP synthesis driven by succinate ox idation in submitochondrial particles from bovine heart was studied at pH 7.4 and 8.8. At the two pH, TFP inhibited ATP hydrolysis. Inorgani c phosphate protected against the inhibiting action of TFP. The result s 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 H2PO 4- is the species that competes with TFP. The effect of TFP on oxidati ve phosphorylation was studied at concentrations that do not produce u ncoupling or affect the aerobic oxidation of succinate (<15 mu M). TFP inhibited oxidative phosphorylation to a higher extent at pH 8.8 than at pH 7.4; this was through a diminution in the V-max, and an increas e in the K-m 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 hydrolysi s; this is more noticeable at pH 8.8, i.e., ATPase activity of soluble Fi remains at about 40% of the activity of the control in a concentra tion range of TFP of 40-100 mu M, whereas in oxidative phosphorylation 14 mu M TFP produces a 60% inhibition of phosphate uptake.