Protonophore uncouplers and the decoupler α,ω-hexadecanedioic acid relieve the succinate-induced blockade of glutamate and malate oxidation in the resting state (state 4).

Theoretical and experimental studies have revealed that in liver mitochondria in the absence of ATP synthesis (state 4), the oxidation of a mixture of succinate with glutamate and malate, like the oxidation of succinate alone, involves only complexes III and IV in the generation of the proton motive force, while complex II, which does not pump protons, oxidizes succinate. Consequently, succinate oxidation suppresses the oxidation of glutamate and malate, likely by inducing reverse electron transport (RET) at complex I and inhibiting NADH oxidation. The concentration of succinate at which its half-maximal effect on blocking glutamate and malate oxidation is observed is 220 ± 25 µM, which corresponds to its concentration in cells of various organs and tissues under physiological conditions. The protonophore uncouplers n-trifluoromethoxycarbonylcyanide phenylhydrazone (FCCP), palmitic acid (PA), and chenodeoxycholic acid (CDCA), provided that they stimulate respiration no more than two-fold alleviate the suppression of glutamate and malate oxidation by succinate. The decoupler α,ω-hexadecanedioic acid (HDA), upon stimulating mitochondrial respiration by 1.5-fold, also alleviates the suppressive effect of succinate on glutamate and malate oxidation. It is noted that, unlike protonophore uncouplers, this effect of HDA may be associated with switching complex III of the respiratory chain to an idle mode of operation. During the oxidation of glutamate and malate, i.e., under conditions of forward electron transport, the protonophore uncouplers FCCP, PA, and CDCA inhibit H