Mitochondrial transporter required for glutathione import into mitochondria (By similarity). Glutathione, which plays key roles in oxidative metabolism, is produced exclusively in the cytosol and is imported in many organelles (By similarity). Mitochondrial glutathione is required for the activity and stability of proteins containing iron-sulfur clusters, as well as erythropoiesis (PubMed:34707288). Abundant expression in bone marrow, spleen, testis and kidney. Highly express in primitive erythroblast that fill yorlk sac blood islands at early somite pair stages, and in fetal liver at 12.5 dpc. Embryonic lethality at dpc 13.5 (PubMed:34707288). Embryos are pale due to a severely anemic phenotype (PubMed:34707288). Conditional deletion in the erythroid lineage also leads to severe anemia, characterized by a complete absence of Ter119(+) cells, iron overload and increased apoptosis in fetal liver cells (PubMed:34707288). Cells lacking both Slc25a39 and Slc25a40 show defects in the activity and stability of proteins containing iron-sulfur clusters (PubMed:34707288). Belongs to the mitochondrial carrier (TC 2.A.29) family.