Oxidation of heme

In the fully reduced model, four electrons are transferred to dioxygen through sequential one-electron oxidations of heme as s iron ion, the Cub ion, the heme a iron ion, and one of the bimetallic center s Cua ions. The sequence of electron transferal differs in the mixed valence model, and a tyrosine radical (tyr) is generated. The proposed formation of a tyrosine radical during catalytic turnover arises from the known post-translational modification in most CcO s in which a covalent bond is formed between the his240 ligand of Cub... 

Heme oxygenase catalyzes the regiospecific oxidation of heme to bili-verdin (Fig. 6) and has been isolated and purified from several sources 247-251). In mammals, the enzyme is membrane-boimd, a complication... 

Fig. 2. The distinct steps in the oxidation of heme to biliverdin catalyzed by heme oxygenase. The substituted carbons of the porphyrin ring are labeled, as are the meso-positions. The oxygens introduced in the catalytic process are shown in bold t3rpe.

Fig. 8. Structure of the product obtained in the HO-l-catalyzed oxidation of heme supported by ethylhydroperoxide.

Bartnicki, E. W., N. O. Belser, and C. E. Castro, Oxidation of heme proteins by alkyl halides A probe for axial inner sphere redox capacity in solution and in whole cells , Biochemistry, 17, 5582-5586 (1978). 

Castro, C. E., and E. W. Bartnicki, Conformational isomerism and effective redox geometry in the oxidation of heme proteins by alkyl halides, cytochrome C, and cytochrome oxidase , Biochem., 14,498-503 (1975). 

Sigman JA, Wang X, Lu Y (2001) Coupled oxidation of heme by myoglobin is mediated by exogenous peroxide. J Am Chem Soc 123 6945-6946... 

When the frilly reduced enzyme is allowed to react with O2, a more complicated sequence of events ensues (Figure 4), since now electrons are available also in the heme a and Cua centers. After formation of the O2 adduct (compound A), the next step is a ca. 30- j,s event which involves electron transfer from the low spin heme to the binuclear site. As reported by Morgan et al., the optical spectrum of the state formed is indistingishable from that of Pm if the absorption change owing to oxidation of heme a is accounted for. In contrast, Einarsdottir et al. have claimed that the spectrum of this Pr state formed from the fully reduced enzyme is different from that of Pm, and that Pr does not represent a stracturally... 

All the products of the oxidation of heme by heme oxygenase are important physiologically. Biliverdin and its reduction product bilirubin are powerful antioxidants and, at nontoxic concentrations, contribute to cellular protection. CO, the second product, also has potent biologic activities, although it is often... 

A (C) It is produced by oxidation of heme, with loss of carbon monoxide (CO)... 

C. Bilirubin is produced by oxidation of heme after its iron is released CO is released in this reaction. Bilirubin diglucuronide is excreted into the bile by the liver. 

The enzymatic oxidation of heme produces CO and biliverdin in equimolar amounts (Chapter 29). The CO is transported via the blood to the lungs, where it is released. Although no cases are known in which endogenous CO proved toxic, this carbon monoxide may contribute significantly to air pollution, particularly in crowded and enclosed areas. 

Biliverdin—A green bile pigment formed from the oxidation of heme. 

It is concluded that it is predominantly only one heme, heme that is reduced by a light flash, and that interheme electron transfer was not observed under the conditions of these experiments. The quinone binding site that serves for reduction of heme by PQ- can also serve in the green dga Chlorella as the site for DNP-INT-sensitive oxidation of pre-reduced cytochrome be (9). The use of this pathway for the oxidation of heme bp would be consistent with the conclusion that the electrogenic step under reducing conditions does not arise from interheme transfer (10). One should note that there has been a report of interheme electron transfer in vitro in the isolated cytochrome b6-/complex (11). 

Fig. 20. Scheme for the autocatalytic oxidation of heme in injured erythrocytes. 

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