Hydroxymethylbilane synthase
Definition:
EC Tree > 2 Transferases > 2.5 Transferring alkyl or aryl groups, other than methyl groups > 2.5.1 Transferring alkyl or aryl groups, other than methyl groups (only sub-subclass identified to date) > 2.5.1.61 hydroxymethylbilane synthase
Hydroxymethylbilane synthase (porphobilinogen deaminase) is the third enzyme of heme/chlorophyll biosynthesis. It stepwise condenses four porphobilinogen molecules, releasing four NH3, and builds a hexapyrrole at the active-site cysteine; the terminal tetrapyrrole is hydrolyzed off to yield hydroxymethylbilane, leaving a dipyrrole cofactor on the enzyme. In the presence of EC 4.2.1.75 uroporphyrinogen-III synthase the bilane cyclizes to uroporphyrinogen-III; without it, it cyclizes spontaneously to uroporphyrinogen-I. It occurs in Bacteria, Eukaryota and Archaea.
Hydroxymethylbilane synthase (porphobilinogen deaminase) is the third enzyme of heme/chlorophyll biosynthesis. It stepwise condenses four porphobilinogen molecules, releasing four NH3, and builds a hexapyrrole at the active-site cysteine; the terminal tetrapyrrole is hydrolyzed off to yield hydroxymethylbilane, leaving a dipyrrole cofactor on the enzyme. In the presence of EC 4.2.1.75 uroporphyrinogen-III synthase the bilane cyclizes to uroporphyrinogen-III; without it, it cyclizes spontaneously to uroporphyrinogen-I. It occurs in Bacteria, Eukaryota and Archaea.
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