Protoheme, biosynthesis

Within the past few years, there has been considerable progress in understanding the role played by the mitochondria in the cellular homeostasis of iron. Thus, erythroid cells devoid of mitochondria do not accumulate iron (7, 8), and inhibitors of the mitochondrial respiratory chain completely inhibit iron uptake (8) and heme biosynthesis (9) by reticulocytes. Furthermore, the enzyme ferrochelatase (protoheme ferro-lyase, EC 4.99.1.1) which catalyzes the insertion of Fe(II) into porphyrins, appears to be mainly a mitochondrial enzyme (10,11,12,13, 14) confined to the inner membrane (15, 16, 17). Finally, the importance of mitochondria in the intracellular metabolism of iron is also evident from the fact that in disorders with deranged heme biosynthesis, the mitochondria are heavily loaded with iron (see Mitochondrial Iron Pool, below). It would therefore be expected that mitochondria, of all mammalian cells, should be able to accumulate iron from the cytosol. From the permeability characteristics of the mitochondrial inner membrane (18) a specialized transport system analogous to that of the other multivalent cations (for review, see Ref. 19) may be expected. The relatively slow development of this field of study, however, mainly reflects the difficulties in studying the chemistry of iron. 

Roy R, Knowles R (1995) Differential inhibition by allylsulfide of nitrification and methane oxidation in freshwater sediment. Appl Environ Microbiol 61 4278 1283 Saiki K, Mogi T, Anraku Y (1992) Heme O biosynthesis in Escherichia coli the cyoE gene in the cytochrome bo operon encodes a protoheme IX famesyl transferase. Biochem Biophys Res Commun 189 1491-1497... 

Biosynthesis synthesis The biosynthesis from protoporphyrin proceeds through chelatization of an iron(ll) ion catalyzed by ferrochelatase (protoheme ferrolyase, EC 4.99.1.1). Tlie H. in red blood particles is degraded to bile pigments after an average life-time of ca. 120 d. 

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