Porphobilinogen (PBG)

This is the intermediate precursor of the porphyrins.

There is a pyrrole ring with acetyl, propionyl, and aminomethyl side chain.

There are four molecules of porphobilinogen condensed to form one molecule of uroporphyrinogen III, this will be converted into:

1. Coproporphyrinogen III.
2. Protoporphyrin IX.
3. Heme.