Activation and inhibition of mitochondrial adenosine triphosphatase by various anions and other agents

Abstract

The activating or inhibiting actions of a variety of anion species and of oligomycin, aurovertin and Dio-9 on the ATPase of a sonic particle preparation of rat liver mitochondria have been characterized by measurements of the relevantV max,K i andK m values. The normalV max was increased by a factor near 7 by the anions: dichromate, chromate, pyrophosphate, orthophosphate, orthoarsenate and sulphate. The fully activating concentration varied from about 2 mM for dichromate to 150 mM for sulphate. The increase inV max was accompanied by a time-dependent decrease in (K i)ADP, but there was no change in (K m)ATP. The increase inV max by the activating anions was abolished by aurovertin; but in presence of oligomycin, the lowV max was increased by the activating anions by the same factor as theV max in absence of oligomycin. Certain anions, notably azide, decreasedV max, but did not affect (K i)ADP or (K m)ATP. The decrease inV max by azide and oligomycin were approximately additive. Even at high concentration, Dio-9 was without detectable effect on the ATPase, but it had a gramicidinlike effect on the intact mitochondria. The specificity of the ATPase for ATP relative to GTP was found to be attributable to the high value of (V max)ATP compared with (V max)GTP. The values of (K m)ATP and (K m)GTP were virtually the same. Some rationalization of these and other supporting observations is attempted in terms of present knowledge of the constitution of the ATPase complex.