This enzyme forms part of the pathway for the biosynthesis of 5-aminolevulinate from glutamate, known as the C5 pathway. The route shown in the diagram
is used in most eubacteria, and in all archaebacteria, algae and plants. However, in the alpha-proteobacteria, EC 18.104.22.168, 5-aminolevulinate synthase, is used in an alternative route to produce the product 5-aminolevulinate from succinyl-CoA and glycine. This route is found in the mitochondria of fungi and animals, organelles that are considered to be derived from an endosymbiotic alpha-proteobacterium. Although higher plants do not possess EC 22.214.171.124, the protistan Euglena gracilis possesses both the C5 pathway and EC 126.96.36.199.