Heme-oxygen complexes

Metabolic degradation of compounds by cyctochromes comprises two important aspects. Initially, the ligand has to be recognized by the enzyme and needs to bind at its active site. Following that, a ligand site is exposed to the heme-oxygen complex... 

It has been shown that the activity of NO synthases is regulated by cofactors calcium binding protein calmodulin and tetrahydrobiopterin (H4B). Abu-Soud et al. [149] have studied the effect of H4B on the activity of neuronal nNOS I, using the isolated heme-containing oxygenase domain nNOSoxy. It was found that nNOSoxy rapidly formed an oxygenated complex in the reaction with dioxygen, which dissociated to produce superoxide (Reaction (6)) ... 

In order to prepare and isolate solid-state, crystalline, oxygenated iron-heme model complexes, chemists learned to synthesize (by self-assembly methods) and oxygenate many types of hindered porphyrins. For instance, capped porphyrins were synthesized by direct condensation of a suitable tetraaldehyde with four pyrrole molecules.37 Picket-fence porphyrins such as I e(TPP)((V-MeIm) (where TPP = meso-tetraphenylporphyrin and /V-Melm = (V-methylimidazole)... 

Synthetic models of myoglobin and hemoglobin are complex molecules that mimic the stereochemical properties of the protein active center [24] and have oxygen affinities similar to those measured for the protein [25-27]. The first heme model that reversibly binds oxygen (i.e. the picket-fence-oxygen complex Fe(TpivPP)(l,2-Melm)(02), shown in Fig. 3.3) was obtained in the early nine-teen-seventies by Collman and coworkers (TpivPP = tetrapivalami-nophenyl porphyrin 2-meIm = 2-methylimidazole) [18]. Research on synthetic models of the protein has led to a deeper understand-... 

In summary, there is still much to understand about the nitrite reduction reaction. The crystal structures have shown how nitrite can bind to the di heme iron and protons can be provided to one of its oxygen atoms from two histidine residues. However, as yet no rapid reaction study has detected the release of product nitric oxide rather than the formation of the inhibitory dead-end ferrous di heme-NO complex. It is also not clear why the rate of interheme electron transfer is so slow over 11 A when nitrite or nitric oxide is the ligand to the d heme. 

Oxygenation potential of heme-type complexes in zeoltie. 211... 

OXYGENATION POTENTIAL OF HEME-TYPE COMPLEXES IN ZEOLITE... 

Naruta, Y., Sasaki, T, Tani, F, Tachi, Y., Kawato, N., and Nakamura N (2001) Heme-Cu complexes as oxygen-activating functional models for the active site of cytochrome c oxidase, J. Inorg. Biochem. 83, 239-46. 

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