A Comparison of the Effects of NN'-Dicyclohexylcarbodi-imide, Oligomycin A and Aurovertin on Energy-Linked Reactions

1. The effects of dicyclohexylcarbodi-imide, oligomycin A and aurovertin on enzyme systems related to respiratory-chain phosphorylation were compared. Dicyclohexylcarbodi-imide and oligomycin A have very similar functional effects, giving 50% inhibition of ATP-utilizing and ATP-generating systems at concentrations below 0.8nmole/mg. of submitochondrial-particle protein. Aurovertin is a more potent inhibitor ofATP synthesis, giving 50% inhibition at 0.2nmole/mg. ofprotein. However, aurovertin is a less potent inhibitor ofATP-utilizing systems: the ATP-driven energy-linked nicotinamide nucleotide transhydrogenase is 50% inhibited at 3*Onmoles/mg. of protein and the ATP-driven reduction ofNAD+ by succinate is 50% inhibited at 0.95nmole/mg. of protein. 2. With EDTA-particles (prepared by subjecting mitochondria to ultrasonic radiation atpH 9 in the presence of 2mM-EDTA) the maximum stimulation of the ATP-driven partial reactions is effected by similar concentrations of oligomycin A and dicylcohexylcarbodi-imide, but the latter is less effective. The stimulatory effects of suboptimum concentrations of dicyclohexylcarbodi-imide and oligomycin A are additive. Aurovertin does not stimulate these reactions or interfere with the stimulation by the other inhibitors. 3. Dicyclohexylcarbodi-imide and oligomycin A stimulate the aerobic energy-linkednicotinamide nucleotidetranshydrogenase ofEDTA-particles, butthe optimum concentration is higher than that required for the ATP-driven partial reactions. Aurovertin has no effect on this reaction. 4. The site of action of dicyclohexylcarbodi-imide is in CFo, the mitochondrial fraction that confers oligomycin sensitivity on F1 mitochondrial adenosine triphosphatase.