Porphobilinogen (PBG) is a pyrrole involved in porphyrin metabolism.
It is generated by aminolevulinate (ALA) and the enzyme ALA dehydratase. PBG is then converted into hydroxymethyl bilane by the enzyme porphobilinogen deaminase, also known as hydroxymethylbilane synthase.
Acute intermittent porphyria causes an increase in urinary porphobilinogen.