Hydroxymethylbilane Synthase

**Definition:** An enzyme that catalyzes the tetrapolymerization of the monopyrrole PORPHOBILINOGEN into the hydroxymethylbilane preuroporphyrinogen (UROPORPHYRINOGENS) in several discrete steps. It is the third enzyme in the 8-enzyme biosynthetic pathway of HEME. In humans, deficiency in this enzyme encoded by HMBS (or PBGD) gene results in a form of neurological porphyria (PORPHYRIA, ACUTE INTERMITTENT). This enzyme was formerly listed as EC 4.3.1.8

**Tree numbers:** - D08.811.913.225.575

**Synonyms:** - Porphobilinogen Ammonia-Lyase - Porphobilinogen Deaminase - Hydroxymethylbilane Synthetase - Preuroporphyrinogen Synthetase - Uroporphyrinogen I Synthase - Pre-uroporphyrinogen Synthetase