Ferroheme

Figure 18.4 Structures of heme/Cu oxidases at different levels of detail, (a) Position of the redox-active cofactors relative to the membrane of CcO (left, only two obligatory subunits are shown) and quinol oxidase (right), (b) Electron transfer paths in mammalian CcO. Note that the imidazoles that ligate six-coordinate heme a and the five-coordinate heme are linked by a single amino acid, which can serve as a wire for electron transfer from ferroheme a to ferriheme as. (c) The O2 reduction site of mammalian CcO the numbering of the residues corresponds to that in the crystal structure of bovine heart CcO. The subscript 3 in heme as and heme 03 signifies the heme that binds O2. The structures were generated using coordinates deposited in the Protein Data Bank, lari [Ostermeier et al., 1997] Ifft [Abramson et al., 2000] (a) and locc [Tsukihara et al., 1996] (b, c).

Yang Q, Khvostichenko D, Atkinson J, Boulatov R. 2008. Simple dimer containing dissocia-tively stable mono-imidazole ligated ferrohemes. Chem Commun (8) 963. 

The singlet (S = 0) state lies about 1000 cm above the ground state triplet (S = 1) in the EPR spectrum of free dioxygen. Transitions associated with triplet oxygen in solution are detectable by EPR at low temperatures, but dioxygen complexes with even electron metal centers (e.g., ferroheme) are not generally observable by this method. Usually, only odd electron systems (Kramers systems) are detectable by magnetic resonance. 

Ferroheme-NO complexes are the best known and most thoroughly studied NO adducts with biochemical relevance. Some of the vast body of existing work... 

Both siroheme enzymes form ferroheme-NO complexes in which the g value anisotropy appears somewhat smaller than in the corresponding complexes of most other enzymes. The EPR spectra of the complexes somewhat resemble the spectra of the high-temperature myoglobin-NO complexes. The hyperfine splitting from the NO nitrogen nucleus is evident at intermediate g values but is not well resolved. These enzymes are capable of reducing NO to ammonia if supplied with low potential reducing equivalents. Other heme proteins also catalyze oxidation reduction reactions with NO. 

In this section, the complex formations and the coordination structures of ferri- and ferro-protoporphyrineIX(ferriheme and ferrohem, respectively) 22 with... 

The n values of the PLL-ferriheme and -ferroheme complexes in Table 4 are equal to 2, and the six-coordinate heme structure is formed preferentially this may be due to an inherent factor in which PLL differs from the other polymer ligands. 

Table 4. Axial coordination number (n) and formation constant (tf) for polymer-ferriheme and -ferroheme complexes 3 4 ... 

Ligand Solvent n Ferriheme Ferroheme K (1/molforn Ferriheme = 1 l2/mol2 forn = 2) Ferroheme... 

In hemoglobin and myoglobin the globin protein protects the ferroheme, which is tucked into a hydrophobic crevice of the protein, known as the heme pocket . 

One of the major difficulties encountered in attempts to prepare 1 1 dioxygen-iron complexes which can desorb molecular oxygen, particularly oxygenated complexes of ferroheme, is the strong driving force toward the irreversible formation of the stable p-oxo ferriheme dimer, as represented in Eq. (11). The oxygenated... 

In a classic experiment Wang97) reported the first synthetic oxygen carrier of Fe(II)porphyrin. He embedded the diethyl ester of ferroheme in a hydrophobic... 

Fig. 21. Schematic diagram of ferroheme derivate embedded in matrix of poly-(styrene) and l-(2-phenylethyl)-imidazole97 ...

Hatano12 dispersed the ferroheme complex of poly(N-vinyl-2-methylimidazole) in fluid paraffin. He reported a reversible change in the visible spectra with respect to oxygen exposure. 

We have studied the oxygenation of ferroheme bound to a polymer ligand in the solid state98. The profiles of oxygen uptake by powders of polymer-heme complexes were measured by volumetry, as shown in Fig. 22. The heme complex embedded in the porous polymer matrix or in the poly(electrolyte) aggregate takes up... 

The oxygenated complex desorbed molecular oxygen on heating under reduced oxygen pressure. Desorption of oxygen, i.e. regeneration of the ferroheme complex,... 

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