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:32499479, PubMed:21252495, PubMed:21653323, PubMed:21309041). Contributes significantly to heme formation during erythropoiesis (PubMed:2050125). 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). 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). glycine + H(+) + succinyl-CoA = 5-aminolevulinate + CO2 + CoA glycine + H(+) + succinyl-CoA = 5-aminolevulinate + CO2 + CoA glycine + H(+) + succinyl-CoA = 5-aminolevulinate + CO2 + CoA glycine + H(+) + succinyl-CoA = 5-aminolevulinate + CO2 + CoA Porphyrin-containing compound metabolism; protoporphyrin-IX biosynthesis; 5-aminolevulinate from glycine: step 1/1. Homodimer (PubMed:32499479). Interacts with SUCLA2 (PubMed:14643893, PubMed:32499479). Interacts with SUCLA2. Localizes to the matrix side of the mitochondrion inner membrane. Localizes to the matrix side of the mitochondrion inner membrane. Erythroid-specific. Erythroid-specific. Erythroid-specific. Erythroid-specific. C-terminus is a mobile self-inhibitory loop which interferes directly with active site. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Gain of function mutations in ALS2 are responsible for XLDPT, but they can also be a possible aggravating factor in congenital erythropoietic porphyria and other erythropoietic disorders caused by mutations in other genes (PubMed:21309041). Belongs to the class-II pyridoxal-phosphate-dependent aminotransferase family. Truncated N-terminus.