ALA synthase
The rate-limiting enzyme in porphyrin and heme biosynthesis is ALA synthase, the enzyme that catalyses glycine and succinyl-CoA into D-Aminolevulinic acid. In humans, transcription of ALA synthase is tightly controlled by the presence of Fe2+-binding elements, to prevent accumulation of porphyrin intermediates in the absence of iron.
ALA synthase removes the carboxyl group from glycine and the CoA from the succinate, forming δ-amino levulinic acid (dALA), so called because the amino group is on the fourth carbon atom in the molecule.
