Hydroxymethylbilane
（重定向自Preuroporphyrinogen）
Hydroxymethylbilane (HMB), also known as preuroporphyrinogen, is a molecule involved in the metabolism of porphyrin. In the third step, it is generated by the enzyme porphobilinogen deaminase, and in the next step the enzyme uroporphyrinogen III synthase converts it into uroporphyrinogen III.