**3. Mitochondrial Carriers Relevant to Mitochondrial Oxidative Phosphorylation**

Oxidative phosphorylation (electron transport-linked phosphorylation) is the route by which ATP is formed as a result of the transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers in the IMM [59]. The oxidative phosphorylation system is composed of the mitochondrial electron transport chain (ETC) and the ATP synthase complex (Complex V) from bacteria to higher eukaryotes [59]. To drive favorable translocation of charged species across the IMM, the ΔΨm and ΔpH generated through the action of the mitochondrial respiratory electron transfer chain could influence the transporter activity. The electrochemical gradient is ultimately used by the ATP synthase to produce ATP. Therefore, the state of oxidative phosphorylation would be expected to affect the kinetic behavior, specificity, transport orientation, and cooperativity of IMM transporters. There are three transport processes directly or indirectly related to mitochondrial oxidative phosphorylation that is mediated by MCs: (1) transport of NAD+, (2) proton translocation, and (3) transport of adenine nucleotides (Figure 3).

**Figure 3.** Mitochondrial carriers relevant to mitochondrial oxidative phosphorylation. (**A**) Sweetlove et al. [60] proposed that the function of UCP1 in photorespiration is in the dissipation of protons generated by the increased flux of NADH to the complex 1 of the electron transport chain (ETC). (**B**) Monne et al. [61] showed that UCP1 and 2 mediate aspartate/glutamate exchange. It was proposed that UCP1/2 play a role in dissipating reducing equivalents across the mitochondrial membrane as part of the malate/aspartate shuttle during photorespiration. (**C**) NDT1 and 2 facilitate the transport of NAD<sup>+</sup> from the cytosol in exchange with ADP or AMP from the mitochondria. ADP/ATP carriers, APCs, ADNT1, and AtBrittle1 mediate the transport of adenine nucleotides. UCP1/2: uncoupling protein 1/2, GDC: glycine decarboxylase complex, GOT: glutamic oxaloacetic transaminase, AACs: ADP/ATP carriers, APCs: ATP/Pi carriers, ADNT1: adenine nucleotide transporter 1, NDT1/2: NAD<sup>+</sup> transporter 1/2.
