Hydroxymethylbilane Synthase (HMBS)

Porphobilinogen deaminase is an enzyme involved in the third step of the metabolism of porphyrin, converting porphobilinogen into hydroxymethyl bilane. The enzyme has the unique cofactor dipyrromethane. Defective activity of this enzyme can lead to the disorder Acute intermittent porphyria.This gene encodes a member of the hydroxymethylbilane synthase superfamily. The encoded protein is the third enzyme of the heme biosynthetic pathway and catalyzes the head to tail condensation of four porphobilinogen molecules into the linear hydroxymethylbilane. Mutations in this gene are associated with the autosomal dominant disease acute intermittent porphyria. Alternatively spliced transcript variants encoding different isoforms have been described.