Aminolevulinic acid synthase

Aminolevulinic acid synthase (ALA synthase, ALAS, or delta-aminolevulinic acid synthase) is an enzyme (EC 2.3.1.37) that catalyzes the synthesis of δ-aminolevulinic acid (ALA) the first common precursor in the biosynthesis of all tetrapyrroles such as hemes, cobalamins and chlorophylls. The reaction is as follows:

succinyl-CoA + glycine ${\displaystyle \rightleftharpoons }$ δ-aminolevulinic acid + CoA + CO₂

This enzyme is expressed in all non-plant eukaryotes and the α-class of proteobacteria and the reaction it catalyses is sometimes referred to as the Shemin pathway for ALA formation. Other organisms produce ALA through a three enzyme pathway known as the C5 pathway. ALA is synthesized through the condensation of glycine and succinyl-CoA. 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. There are two forms of ALA synthase in the body. One form is expressed in red blood cell precursor cells (ALAS2), whereas the other (ALAS1) is ubiquitously expressed throughout the body. The red blood cell form is coded by a gene on chromosome X, whereas the other form is coded by a gene on chromosome 3.

The disease X-linked sideroblastic anemia is caused by mutations in the ALA synthase gene on chromosome X, whereas no diseases are known to be caused by mutations in the other gene. Gain of function mutations in the erythroid specific ALA synthase gene have been shown recently to cause a previously unknown form of porphyria known as X-linked-dominant protoporphyria.