Electroneutral antiporter that mediates the transport of adenine nucleotides through the inner mitochondrial membrane. Originally identified as an ATP-magnesium/inorganic phosphate antiporter, it also acts as a broad specificity adenyl nucleotide antiporter. By regulating the mitochondrial matrix adenine nucleotide pool could adapt to changing cellular energetic demands and indirectly regulate adenine nucleotide-dependent metabolic pathways (PubMed:15123600). Also acts as a regulator of mitochondrial calcium uptake and can probably transport trace amounts of other divalent metal cations in complex with ATP (PubMed:24430870, PubMed:28695448). In vitro, a low activity is also observed with guanyl and pyrimidine nucleotides (PubMed:15123600). {ECO:0000269|PubMed:15123600, ECO:0000269|PubMed:24430870, ECO:0000269|PubMed:28695448}. This is the function of SLC25A23 (solute carrier family 25 member 23, ENSG00000125648).