Mitochondrial S-adenosyl-L-methionine/S-adenosyl-L- homocysteine antiporter. Mediates the exchange of cytosolic S-adenosyl- L-methionine, the predominant methyl-group donor for macromolecule methylation processes, for mitochondrial S-adenosylhomocysteine(SAH), a by-product of methylation reactions. {ECO:0000269|PubMed:14674884, ECO:0000269|PubMed:26522469, ECO:0000269|PubMed:35024855}. This is the function of SLC25A26 (solute carrier family 25 member 26, Ensembl gene identifier ENSG00000144741).