Cysteine thiolate Cytochrome

The resting state, the low-spin Fe complexes of the family of monooxygenase and oxidase enzymes known as the cytochromes P450 see Iron Heme Proteins, Mono- Dioxygenases), have one cysteine thiolate as the proximal ligand T258 water molecule as the distal... 

A recent summary25 of the activation of O2 by cytochrome P-450 (an iron(III)-heme protein with a axial cysteine thiolate ligand) concludes that the reactive form of this mono-oxygenase also contains an oxene-ferryl group (RS)(por)FeV=O. The mono-oxygenase chemistry of cytochrome P-450 has been modeled via the use of (TPP)Fei lCl(TPP=tetraphenylporphyrin) and (OEP)Fe JCl (OEP=octaethylporphyrin) with peracids,26,27 iodosobenzene,26,27... 

Ferryl complexes have been implicated in the reaction mechanisms of peroxidases and cytochromes P450. 38,1596 Pqj. horseradish peroxidase, two intermediates are spectroscopically detectable. Compound I, formed upon addition of peroxide to the resting Fe form of the enzyme, is a green species that is formally two oxidation levels higher than the resting state, and is widely believed to consist of an (Fe =0) + unit complexed by a porphyrin jt-cation radical. The [(P" ) Fe =0]+ complexes are discussed in Section 9. Compound II, which is red, and is obtained upon one-electron reduction of Compound I, also possesses a (Fe =0) + unit, in this case complexed by a normal porphyrin dianion, PFe =0. The fifth ligand, provided by the protein in the various enzymes, is a cysteine thiolate for the cytochromes nitric oxide synthases... 

Axial ligands of heme-containing enzymes, such as a cysteine thiolate in cytochromes P450 and chloroperoxidases, a histidine imidazole in peroxidases, and a tyrosine phenolate in catalases, are... 

Fig. 1 Reactions involving molecular oxygen and its reduced congeners in heme proteins. Reactions where equilibria are manifest are indicated as such. In globins, peroxidases, cytochrome oxidases, and heme oxygenases, the axial ligand X is a protein-derived histidine in catalases, X is a tyrosine phenolate in chloroperoxidases and cytochromes P450, X is a cysteine thiolate...

Liu HI, Sono M, Kadkhodayan S, Hager LR Hedman B, Hodgson KO, Dawson JH (1995) X-ray absorption near edge studies of cytochrome P-450-cam, chlo-roperoxidase, and myoglobin. Direct evidence for the electron releasing character of a cysteine thiolate proximal ligand. J Biol Chem 270 10544-10550... 

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