Protoporphyrins

**Definition:** Porphyrins with four methyl, two vinyl, and two propionic acid side chains attached to the pyrrole rings. Protoporphyrin IX occurs in hemoglobin, myoglobin, and most of the cytochromes.

**Tree numbers:** - D03.383.129.578.840.500.725 - D03.633.400.909.500.725 - D04.345.783.500.725 - D23.767.727.725