Porphyrin ferrous protoporphyrin

The ferrous complex of octaethyl porphyrin in SDS micelles has been characterized as four coordinated (S = 1) ferrous heme species and is similar to that observed for the ferrous protoheme complex in CTAB. It is noted that ferrous complexes of natural porphyrins cannot be stabilized in aqueous SDS micelles, and much larger aqueous micelles like CTAB were needed to stabilize various ferrous protohemes. This indicates that the environment around the octaethyl porphyrin complex in aqueous SDS is more hydrophobic than that of the analogous natural heme species, suggesting that the OEP moiety is embedded much deeper inside the micellar hydrophobic cavity than the protoporphyrin analogue. 

The micelle-encapsulated six coordinated bis(pyridinato) iron(II) complexes of protoporphyrin and OEP have been reported by addition of pyridine to the four coordinate ferrous complex in aqueous micellar solution. The optical spectrum of [Fe(II)(PP)(Py)2] in micelle (Fig. 10) is identical to S = 0 six-coordinate bis(pyridinato) iron(II) porphyrin complex [3]. The magnetic moment measurements in solution confirm their diamagnetic nature. The HNMR spectra are also characteristic low-spin iron(II) resonances (S = 0) with shifts lying in the diamagnetic region (Table 2). 

FIGURE 5-1 Heme. The heme group is present in myoglobin, hemoglobin, and many other proteins, designated heme proteins. Heme consists of a complex organic ring structure, protoporphyrin IX, to which is bound an iron atom in its ferrous (Fe2+) state, (a) Porphyrins, of which protoporphyrin IX is only one example, consist of four pyr-... 

Heme is a complex of protoporphyrin IX and ferrous iron (Fe2+).The iron is held in the center of the heme molecule by bonds to the four nitrogens of the porphyrin ring. The Fe2+ can then form two additional bonds, including one to molecular oxygen. 

The insertion of ferrous iron into the porphyrin ring in the biosynthesis of heme is catalyzed by the enzyme ferrochelatase. A deficiency in ferrochelatase activity results in an accumulation or the excretion of unchelated protoporphyrin in patients with erythrohepatic protoporphyria. Ferrochelatase catalyzes the synthesis of a range of metalloporphyrins,628 and, for example, produces zinc protoporphyrin in erythrocytes of patients with iron-deficiency anaemia. 

FECH (also known as heme synthase) is an iron-sulfur protein located in the inner mitochondrial membrane. This enzyme inserts ferrous iron into protoporphyrin to form heme During this process, two hydrogens are displaced from the ring nitrogens. Other metals in the divalent state will also act as substrate, yielding the corresponding chelate (e.g., incorporation of Zn into protoporphyrin to yield zinc protoporphyrin). In iron-deficient states Zn successfully competes with Fe in developing red cells so that the concentration of zinc protoporphyrin in erythrocytes increases. Furthermore, other dicarboxylic porphyrins will also serve as substrates (e.g., mesoporphyrin). 

Four of the six valencies of the central iron atom are held in the planar porphyrin ring, and when heme and hematin are in true solution the fifth and sixth bonds completing an octahedral complex are assumed to be occupied by water molecules. These compounds, i.e., heme and hemin, can be represented as H2OFepH20 and H2()Fe,+TI20, where Fep and Fep+ represent ferrous and ferric protoporphyrin respectively. Ionization of one of the water molecules attached to heme in solution... 

Due to the many biological functions of ferrous heme nitrosyls, many corresponding model complexes have been synthesized and structurally and spectroscopically characterized, viz. tetraphenylporphyrin (TPPH2), octaethylporphyrin (OEPH2) and protoporphyrin IX diester (PPDEH2), ms o-tetrakis (4-carboxyphenyl) porphyrin (TCPP), meso-tetrakis [4-(N,N,N-trimethyl) aminophenyl] porphyrin (TTMAPP),... 

When ferrous iron is inserted into protoporphyrin, the ubiquitous iron porphyrin or heme is formed. Because of the resonating structure, an electron donor or acceptor molecule need not come in contact with the iron atom directly to oxidize or reduce the iron atom it is probably sufficient that contact be made with any portion of the resonating molecule for the iron atom to be oxidized or reduced. The oxidative properties of the iron atom in heme are modified by the iron being held in this ring and are further modified by the heme being attached to specific proteins. In nature the other metal that complexes with protoporphyrin is magnesium Mg protoporphyrin is an intermediate compound in the biosynthetic chain of chlorophyll synthesis. The movements of the ir electrons in the porphyrin are undoubtedly intimately connected with the functioning of the heme and chlorophyll structures, but of this we know very little. 

Synthesis of haem is readily accomplished from simple precursors. In the first step of porphyrin synthesis succinyl-CoA, which is produced in the citrate cycle and during the metabolism of various amino acids, is condensed with glycine to give d-aminolaevulinic acid, and it is this reaction which is rate-controlling. Subsequently two molecules of d-aminolaevulinic acid condense to form porphobilinogen and four molecules of porphobilinogen undergo a series of reactions to produce protoporphyrin which combines with ferrous ions to form haem. 

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