Oxygenase metalloenzyme

Then later in an aerobic world with mainly iron(III) both, zinc peptidases and iron oxygenases, evolved from these ancestors. Today nature mainly uses zinc centers in metalloenzymes for the hydrolyses of peptide bonds (99,J00). In the commonly accepted mechanism for zinc peptidases, zinc(II) has two tasks It polarizes the carbonyl functionality of the peptide bond that is going to be cleaved and it supports the deprotonation of the coordinated water nucleophile. 

A large number of investigations of the mechanism of electron transfer reactions of macromolecule-metal complexes in biological systems has been reported. These investigations were concerned with not only natural metalloenzymes such as cytochromes, ferredoxin, blue coppers, oxygenase, peroxidase, catalase, hemoglobin, and ruberodoxin, but also modified metalloenzymes 47). 

It should be pointed out that no X-ray structure of a metalloenzyme capable of catalyzing a redox reaction has been reported. Thus, the detailed environment of the metal ion in most redox enzymes is largely unknown. The porphyrin ring system is known to be present in many metalloenzymes, including certain oxygenases. These ligands are probably intimately involved in catalysis carried out by these enzymes. 

The pterin-dependent oxygenases, typified by the aryl amino acid hydroxylases, are a small family of closely related enzymes, which are essential to mammalian physiology. This class of metalloenzymes employs tetrahydrobiopterin (BH4) as a two-electron donating cofactor for the activation of O2. Members of this class include phenylalanine (PheH), tyrosine (TyrH) and tryptophan (TrpH) hydroxylases, which effect regiospecific aromatic hydroxylations of the namesake amino acids. 

Oxygenases can be classified into three groups based on the co-factor required for catalytic activity of the enzyme. One is the transition-metal free enzyme containing an organic prosthetic group such as flavin, but oxidation of unactivated C-H bonds by this enzyme has not yet been found. The other two are metalloenzymes containing copper or iron. Despite the fact that these enzymes are largely distributed in nature, the molecular mechanisms of their reactions are known in considerably less detail. Elucidation of this... 

Oxidation. Since some metalloenzymes such as cytochrome P-450 and methane mono-oxygenase can selectively oxidize alkanes with dioxygen, there are many approaches that mimic the reactivity of these metalloenzymes using various artificial metal complexes (1,23,24). The first approach is to combine dioxygen and reducing agents in the presence of metal complexes (eq. (12)). 

This trend is due obviously to the relevance of catalytic oxidation to biological processes such as dioxygen transport, and the action of oxygenase and oxidase enzymes related to metabolism. The stmctural and functional modeling of metalloenzymes, particularly of those containing iron and copper, by means of low-molecular complexes of iron, copper, mthenium, cobalt, manganese, etc., have provided a wealth of indirect information helping to understand how the active centers of metalloenzymes may operate. 

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