Tetrapyrrole biosynthesis, glutamate-1-semialdehyde aminotransferase (IPR004639)

Short name: 4pyrrol_synth_GluAld_NH2Trfase

Overlapping homologous superfamilies

Family relationships


Tetrapyrroles are large macrocyclic compounds derived from a common biosynthetic pathway [PMID: 16564539]. The end-product, uroporphyrinogen III, is used to synthesise a number of important molecules, including vitamin B12, haem, sirohaem, chlorophyll, coenzyme F430 and phytochromobilin [PMID: 17227226].

  • The first stage in tetrapyrrole synthesis is the synthesis of 5-aminoaevulinic acid ALA via two possible routes: (1) condensation of succinyl CoA and glycine (C4 pathway) using ALA synthase (EC:, or (2) decarboxylation of glutamate (C5 pathway) via three different enzymes, glutamyl-tRNA synthetase (EC: to charge a tRNA with glutamate, glutamyl-tRNA reductase (EC: to reduce glutamyl-tRNA to glutamate-1-semialdehyde (GSA), and GSA aminotransferase (EC: to catalyse a transamination reaction to produce ALA.

  • The second stage is to convert ALA to uroporphyrinogen III, the first macrocyclic tetrapyrrolic structure in the pathway. This is achieved by the action of three enzymes in one common pathway: porphobilinogen (PBG) synthase (or ALA dehydratase, EC: to condense two ALA molecules to generate porphobilinogen; hydroxymethylbilane synthase (or PBG deaminase, EC: to polymerise four PBG molecules into preuroporphyrinogen (tetrapyrrole structure); and uroporphyrinogen III synthase (EC: to link two pyrrole units together (rings A and D) to yield uroporphyrinogen III.

  • Uroporphyrinogen III is the first branch point of the pathway. To synthesise cobalamin (vitamin B12), sirohaem, and coenzyme F430, uroporphyrinogen III needs to be converted into precorrin-2 by the action of uroporphyrinogen III methyltransferase (EC: To synthesise haem and chlorophyll, uroporphyrinogen III needs to be decarboxylated into coproporphyrinogen III by the action of uroporphyrinogen III decarboxylase (EC: [PMID: 11215515].

This entry represents glutamate-1-semialdehyde (GSA) aminotransferase (EC:, which catalyse a transamination reaction to produce 5-aminoaevulinic acid during the first stage of tetrapyrrole biosynthesis by the C5 pathway [PMID: 11215515, PMID: 15890644]. This enzyme has a high degree of similarity to amino acid transaminases, and is classed as a class III aminotransferase.

GO terms

Biological Process

GO:0033014 tetrapyrrole biosynthetic process

Molecular Function

GO:0042286 glutamate-1-semialdehyde 2,1-aminomutase activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.