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. 2012 Jan 18;3:2. doi: 10.3389/fpls.2012.00002

Figure 2.

Figure 2

Schematic overview of a plant cell detail presenting the occurrence of MCF carriers in membranes of different compartments. MCF proteins were identified in the inner membrane of mitochondria and plastids, in the thylakoids, in the endoplasmic reticulum (ER), in peroxisomes, and in the plasma membrane (separating the cytosol and the apoplast). Three ADP/ATP carriers (AAC1–3), the ATP/AMP carrier (ADNT1), putative ATP–Mg/Pi carriers (APC?), and the NAD/adenine nucleotide exchanger mediate the passage of ATP, ADP, AMP, or of the adenylated cofactor NAD across the inner mitochondrial membrane. The mitochondrial transport of carboxylates is mediated by three dicarboxylate carriers (DIC1–3), by a dicarboxylate/tricarboxylate carrier (DTC), and by a carrier probably specific for succinate/fumarate exchange. The controlled flux of protons reduces the mitochondrial membrane potential (ΔΨ) and is catalyzed by two proven and one predicted uncoupling protein (UCP1–3). The transport of the cofactor thiamine pyrophosphate in exchange with thiamine monophosphate or (d)NTPs is probably catalyzed by a postulated mitochondrial thiamine pyrophosphate carrier (TPC?). Basic amino acids leave and enter the mitochondrion via the carriers BAC1 and BAC2 (BAC1–2) and the carnitine/ac(et)ylcarnitine carrier and the S-adenosylmethionine carrier (SAMC1) provide carbon moieties to the organelle. The three carriers PiC1–3 allow the net import of phosphate that can act as substrate of ATP synthesis and as counter exchange substrate of other MCF proteins. Plastids also harbor MCF proteins. An adenine nucleotide exporter (pANT1), a NAD/adenine nucleotide exchanger (NDT1), a possible folate carrier (FOLT1), and a Mitoferrin-like protein reside in the inner envelope membrane and provide important substrates and cofactors to the plastid. In addition to its localization in mitochondria, the carrier SAMC1 was also identified in the plastid. ATP provision to the thylakoid and to the ER is probably facilitated by the respective ATP/ADP exchangers – TAAC and ER-ANT1. Peroxisomes contain specific adenine nucleotide carriers (PNC1/2) as well as the NAD transporter PXN. In the plasma membrane, the protein PM-ANT1 might be involved in the provision of extracellular ATP.