Protoporphyrin reactions involving

The final step in heme synthesis involves the incorporation of ferrous iron into protoporphyrin in a reaction catalyzed by ferrochelatase (heme synthase), another mitochondrial enzyme (Figure 32-4). 

Taking protoporphyrin-IX (19) as the inexpensive commercially available starting material for porphyrin manipulations, the common substituent reactions are shown in Scheme 8. Protoporphyrin-IX is usually obtained simply by demetallation of hemin, the most efficient route (which provides the dimethyl ester, ready for chromatographic purification) involving treatment with iron(II) sulfate in methanol containing HC1 gas. 

Structure of protoporphyrin IX. This coenzyme acts in conjunction with a number of different enzymes involved in oxidation and reduction reactions. 

We must assume, then, that the rate-limiting step is virtually independent of the above parameters. Nor can it be involved in the redox-dependent rearrangement of iron-protoporphyrin since the reactions with H2O2 and CH3OOH are faster than those with EtOOH or CH3CO3H. 

Perhaps the best-characterized example of this mechanism involves the synthesis of heme cofactors and their subsequent incorporation into various hemoproteins (see Iron Heme Proteins Electron Transport). Succinctly, enzyme-catalyzed reactions convert either succinyl-CoA or glutamate into 5-ammolevulinic acid. This molecule is further converted through a series of intermediates to form protoporphyrin IX, the metal-ffee cofactor, into which Fe is inserted by ferrochelatase. Analogous reactions are required for the synthesis of other tetrapyrrole macrocycles such as the cobalamins (see Cobalt Bu Enzymes Coenzymes), various types of chlorophylls, and the methanogen coenzyme F430 (containing Co, Mg, or Ni, respectively). Co- and Mg-chelatases have been described for insertion of these metals into the appropriate tetrapyrrolic ring structures. ... 

---