Nonheme enzymes activity

Costas, M., M. P. Mehn et al. (2004). Dioxygen activation at mononuclear nonheme iron active sites Enzymes, models, and intermediates. Chem. Rev. 104(2) 939-986. 

On the basis of the structure of their active site, catalases may be classified as heme or nonheme enzymes. Those that contain heme iron are efficient catalysts, operating close to the diffusion limit, 108M 1sec 1. In iron catalases the metal is coordinated by four heme nitrogens and a proximal Tyr residue, which occupies the fifth coordination site. A catalytically required His is found on the distal side of the heme. In addition, a water molecule has also been observed close to the iron sixth coordination site. 

The following highlights are in the authors opinion the most significant advances in the area of model chemistry for diiron enzymes. This article endeavors to review recent developments in nonheme model chemistry with emphasis on well defined structurally characterized synthetic models. Their spectroscopic properties will be discussed along with their relevance to the enzyme active sites and the parallels of their reactivities as they relate to these enzymes. 

For nonheme enzymes that fiuther activate dioxygen, it is apparent that the diferrous forms also bind O2 to eventually generate the active species responsible for the oxidative transformations. In the case of MMO, the first intermediate has been labeled compound P (Scheme 2), which subsequently converts to compound Q both are kinetically competent to hydroxylate methane. In the case of RNR, compound X (Scheme 1) is responsible for the one-electron oxidation of a tyrosine residue to generate a tyrosyl radical. Based on chemical considerations and its Mossbauer properties, it has been proposed that compound P is a diferric peroxide species. To date, three model complexes of compound P, with comparable spectroscopic properties, have been structurally characterized (Figure g). In two of these models O2 is bound in a cis... 

A wide range of soluble redox enzymes contain one or more intrinsic [2Fe-2S]2+ +, [3Fe-4S]+ , or [4Fe S]2+ + clusters that function in electron transport chains to transfer electrons to or from nonheme Fe, Moco/Wco, corrinoid, flavin, thiamine pyrophosphate (TPP), Fe S cluster containing, or NiFe active sites. Many have been structurally and spectroscopically characterized and only a few of the most recent examples of each type are summarized here. Dioxygenases that function in the dihydroxylation of aromatics such as benzene, toluene, benzoate, naphthalene, and phthalate contain a Rieske-type [2Fe-2S] + + cluster that serves as the immediate electron donor to the monomeric nonheme Fe active site see Iron Proteins with Mononuclear Active Sites). The xanthine oxidase family of molybdoenzymes see Molybdenum MPT-containing Enzymes) contain two [2Fe-2S] + + clusters that mediate electron transfer between the Moco active site and the Other soluble molybdoen-... 

The catalases catalyze the disproportionation of hydrogen peroxide (equations). Most catalases contain the iron-protoporphyrin IX prosthetic group see Iron Heme Proteins, Peroxidases, Catalases Catalase-peroxidases). However, some bacteria are able to synthesize catalases that are not inhibited even by millimolar concentrations of azide and cyanide, suggesting that some catalases are nonheme enzymes it is now known that these enzymes possess a dinuclear Mn active site. 

Dioxygen activation at mononuclear nonheme iron active sites (enzymes, models, and intermediates with pyridines as ligands) 04CRV939. 

Computational Studies of the Catalytic Activity of Heme and Nonheme Enzymes... 

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