Mitochondrial glycine transporter that imports glycine into the mitochondrial matrix. Plays an important role in providing glycine for the first enzymatic step in heme biosynthesis, the condensation of glycine with succinyl-CoA to produce 5-aminolevulinate (ALA) in the mitochondrial matrix. Required during erythropoiesis. May play a role as pro-apoptotic protein that induces caspase-dependent apoptosis. glycine(in) = glycine(out) At 24 hours post-fertilization, expressed predominantly in posterior blood island, posterior cardinal vein and circulating blood, as well as in somites, brain and retina. At 34 hours post-fertilization, becomes restricted to posterior blood island and circulating blood. Fishes lacking both slc25a38a and slc25a38b display anemia. Belongs to the mitochondrial carrier (TC 2.A.29) family. SLC25A38 subfamily.