(S)-4-amino-5-oxopentanoate = 5-aminolevulinate Porphyrin-containing compound metabolism; protoporphyrin-IX biosynthesis; 5-aminolevulinate from L-glutamyl-tRNA(Glu): step 2/2. Porphyrin-containing compound metabolism; chlorophyll biosynthesis. Homodimer. Strongly expressed in leaves of etiolated plantlets independently of light treatment and, to a much lesser extent, in leaves of mature plants. Belongs to the class-III pyridoxal-phosphate-dependent aminotransferase family. HemL subfamily.