The function of ALAS2 (5'-aminolevulinate synthase 2, ENSG00000158578) is as follows. Catalyzes the pyridoxal 5'-phosphate (PLP)-dependent condensation of succinyl-CoA and glycine to form aminolevulinic acid (ALA), with CoA and CO2 as by-products (PubMed:14643893, PubMed:21252495, PubMed:21309041, PubMed:21653323, PubMed:32499479, PubMed:34492704). Contributes significantly to heme formation during erythropoiesis (PubMed:2050125). {ECO:0000269|PubMed:14643893, ECO:0000269|PubMed:21252495, ECO:0000269|PubMed:21309041, ECO:0000269|PubMed:21653323, ECO:0000269|PubMed:32499479, ECO:0000269|PubMed:34492704, ECO:0000303|PubMed:2050125}. [Isoform 3]: Catalyzes the pyridoxal 5'-phosphate (PLP)- dependent condensation of succinyl-CoA and glycine to form aminolevulinic acid (ALA), with CoA and CO2 as by-products (PubMed:14643893). Catalytic activity is 75-85% of isoform 1 activity (PubMed:14643893). . [Isoform 4]: Catalyzes the pyridoxal 5'-phosphate (PLP)- dependent condensation of succinyl-CoA and glycine to form aminolevulinic acid (ALA), with CoA and CO2 as by-products (PubMed:14643893). Catalytic activity is 65-75% of isoform 1 activity (PubMed:14643893). .