On the mechanism of maleate action on rat kidney mitochondria. Effect on substrate-level phosphorylation.

1. Maleate inhibits the substrate-level phosphorylation linked to anaerobic dismutation of 2-oxoglutarate in rat kidney mitochondria. 2. Phosphate and magnesium diminish the inhibitory effect of maleate. Arsenate also relieves the inhibition of 2-oxoglutarate consumption but only at low (1 mM) phosphate concentration; at higher concentrations, the action of phosphate and arsenate is competitive. 3. Acetoacetate, malonate and succinate, the substrates of CoA-transferase, relieve the inhibition of 2-oxoglutarate metabolism by maleate both in the respiring mitochondria and in the "anaerobic" system containing antimycin and rotenone. 4. The interference in succinyl-CoA metabolism by maleate is discussed as a possible mechanism of the inhibitory action of this compound.