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. glycine + H(+) + succinyl-CoA = 5-aminolevulinate + CO2 + CoA Porphyrin-containing compound metabolism; protoporphyrin-IX biosynthesis; 5-aminolevulinate from glycine: step 1/1. Homodimer. Localizes to the matrix side of the mitochondrion inner membrane. Ubiquitous. Belongs to the class-II pyridoxal-phosphate-dependent aminotransferase family.