Porphobilinogen

 ( Metabolism ) 

Porphobilinogen ( PBG) is an organic compound that occurs in living organisms as an intermediate in the biosynthesis of , which include critical substances like hemoglobin and chlorophyll.

The structure of the molecule can be described as molecule of pyrrole with sidechains substituted for hydrogen atoms at positions 2, 3 and 4 in the ring (1 being the nitrogen atom); respectively, an aminomethyl group , an acetic acid (carboxymethyl) group , and a propionic acid (carboxyethyl) group .

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Biosynthesis In the first step of the porphyrin biosynthesis pathway, porphobilinogen is generated from aminolevulinate (ALA) by the enzyme ALA dehydratase.

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Metabolism In the typical porphyrin biosynthesis pathway, four molecules of porphobilinogen are concatenated by carbons 2 and 5 of the pyrrole ring (adjacent to the nitrogen atom) into hydroxymethyl bilane by the enzyme porphobilinogen deaminase, also known as hydroxymethylbilane synthase.

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Pathologies Acute intermittent porphyria causes an increase in urinary porphobilinogen.

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