ABSTRACT
Once the protoporphyrin IX is obtained, ferrochelates are needed to catalyze the insertion of the metal ion. It has been proposed that ferrochelates first bind ferrous iron and then the porphyrin substrate. Metallation occurs when the macrocycle is bent, allowing metal insertion concomitant with proton release from the porphyrin. Once the heme is formed it becomes planar and is released as product [16]. The resulting heme b not only is incorporated directly into 6-type heme proteins but also serves as precursor for the formation of the hemes a, c, d , and o, while heme di and siroheme are formed in pathways that branch off from the above-described pathway subsequent to the first three common steps following formation of 5-aminolevulinate.
