Hemoproteins-peroxide complexes

A possible model of hemoprotein-peroxide complexes formed in an iron-tetraphenylporphyrin system. Biochem. Biophys. Res. Commun. 135, 972-978. 

Jinno, J., M. Shigematsu, K. Tajima, H. Sakurai, H. Ohya-Nishiguchi, and K. Ishizu (1991). Coordination structure and chemical reactivity of hemoprotein-butyl peroxide complex. Biochem. Biophys. Res. Commun. 176, 675—681. 

Heme (C34H3204N4Fe) represents an iron-porphyrin complex that has a protoporphyrin nucleus. Many important proteins contain heme as a prosthetic group. Hemoglobin is the quantitatively most important hemoprotein. Others are cytochromes (present in the mitochondria and the endoplasmic reticulum), catalase and peroxidase (that react with hydrogen peroxide), soluble guanylyl cyclase (that converts guanosine triphosphate, GTP, to the signaling molecule 3, 5 -cyclic GMP) and NO synthases. 

Answers to these questions were initiated over a decade ago during our studies on catalase (CAT) and horseradish peroxidase (HRP) (30). Both native enzymes are ferric hemoproteins and both are oxidized by hydrogen peroxide. These oxidations cause the loss of two electrons and generate active enzymatic intermediates that can be formally considered as Fe + complexes. 

It has been shown above that the catalytic action of catalase and peroxidase is intimately connected with the ability of these hemoproteins to form complexes with hydrogen peroxide (or alkyl peroxides). By choosing the experimental conditions the existence of three different complexes can be demonstrated spectroscopically. The chemical nature of these complexes is as yet unknown, and mechanisms have been represented as bimolecular reactions between substrate and complex. 

It is the reaction of the ferric forms of these hemoproteins with hydrogen peroxide that provides the sharpest contrast to ionic iron. Complexes are formed in both systems. Although ferric ion only gives an ion pair complex Fe02H2+, whereas peroxidase can give three com-... 

Adams, P.A. and J. Louw (1995). Dioxygen bond scission and heme degradation in hemoproteins A kinetic study of chemical model systems using fer-rimyoglobin and hemepeptide Non-hemepeptide complexes as catalysts for peroxidasic reduction of hydrogen peroxide. J. Chem. Soc. Perkin Trans. 2, 1683-1690. 

The oxidation of iodide is performed by enzymes of the peroxidase type (Morrison, 1980), mainly lactoperoxidase, but also by horseradish peroxidase, microperoxidase and chloroperoxidase, which are hemoproteins with tetrapyr-rolic cores chelating iron. These enzymes are active in the presence of small amounts of hydrogen peroxide or glucose oxidase. They form a first complex with H2O2 that... 

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