Partial Resolution of the Enzymes Catalyzing Oxidative Phosphorylation

Abstract

1. A mitochondrial membrane fraction from beef heart (TUA-CF0) was prepared from submitochondrial particles (TUA-particles) by fractionation with ammonium sulfate in the presence of 2% cholate. TUA-CF0 conferred rutamycin or dicyclohexylcarbodiimide (DCCD) on soluble, mitochondrial ATPase (F1) provided that the rutamycin sensitivity factor (Fc) and phospholipids were added. 2. In the absence of Fc and phospholipids, binding of F1 to TUA-CF0 took place with only a partial recovery of ATPase activity. On addition of Fc, a pronounced masking of this ATPase activity was observed. Reactivation of ATPase activity, which was now sensitive to rutamycin and DCCD, was achieved by addition of crude soybean phospholipids. 3. Some purified phospholipids, such as phosphatidylserine and cardiolipin, gave full reactivation of the masked ATPase activity, but low rutamycin sensitivity. Other phospholipids, e.g. phosphatidylethanolamine, gave only partial activation but high rutamycin sensitivity. 4. Exposure of TUA-CF0 or Fc to mild heating (55°) prevented the masking of added F1. Thus it appears that, like rutamycin sensitivity, the masking of the ATPase activity is dependent on two factors: one in the particles, the other in Fc.