Iron active

In order to understand the reason for such a beneficial N2O oxidizing effect, a detailed mechanism of its decomposition as a stage supplying oxygen to the surface has been studied [4,12]. This study revealed a special type of iron active sites in ZSM-5 matrix (called a-sites), which decompose N2O producing a new oxygen form (a-form) ... 

According to the following evidences, a-sites are most probably di-iron complexes similar to the di-iron active sites of methane monooxygenase ... 

Metalloenzymes with non-heme di-iron centers in which the two irons are bridged by an oxide (or a hydroxide) and carboxylate ligands (glutamate or aspartate) constitute an important class of enzymes. Two of these enzymes, methane monooxygenase (MMO) and ribonucleotide reductase (RNR) have very similar di-iron active sites, located in the subunits MMOH and R2 respectively. Despite their structural similarity, these metal centers catalyze very different chemical reactions. We have studied the enzymatic mechanisms of these enzymes to understand what determines their catalytic activity [24, 25, 39-41]. 

Ribonucleotide reductase is responsible for the conversion of the four biological ribonucleotides (RNA) into their corresponding deoxy forms (DNA). Although RNR is not an oxygenase during its primary catalyzed reaction (the conversion of ribonucleotides), it activates oxygen to generate a stable tyrosyl radical that is essential to the overall mechanism [46 49]. The common link between the chemistry of MMO and RNR is the activation of O2 by the di-iron active site. 

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. 

Que, L. and R. Y. N. Ho (1996). Dioxygen activation by enzymes with mononuclear non-heme iron active sites. Chem. Rev. 96(7) 2607-2624. 

Saxe JP, Lubenow BL, Chiu PC, Huang CP, Cha DK (2006) Enhanced biodegradation of azo dyes using an integrated elemental iron-activated sludge system effects of physical-chemical parameters. Wat Env Res 78 26-30... 

A voltage forms between regions of higher irons activity u and regions of lower iron activity a2 (i.e. between regions of high purity and low iron purity) see Figure 7.14. We can write a schematic for a microscopic portion of the iron surface as ... 

The cytotoxicity of BLM is believed to result from its ability to bind iron, activate oxygen, and form an activated BLM (Fe-114) (556) which cleaves DNA and possibly RNA (557). The ability of the Fe(II)-BLM complex to bind to oxygen and produce oxygenated BLM species such as 02-Fe(III)-BLM or 02-Fe(II)-BLM may be due to the presence of delocalized 77-electrons around the iron and the strong iron-pyrimidine 77-back-bonding (558, 559). Oxygenated BLM accepts an additional electron to form activated low-spin ferric-peroxide-BLM (Oi -Fe(III)-BLM) (558, 559). The structural features of Fe-BLM responsible for DNA (or RNA) degradation remain unclear (560). Bleo-... 

Figure 13.22 The 02 complex of naphthalene dioxygenase with the substrate analogue indole bound. Asp205 connects the Rieske [2Fe-2S] centre (located in a neighbouring subunit) to the mononuclear iron active site. (From Koehntop et al., 2005. With kind permission of Springer Science and Business Media.)...

It is interesting that nature has developed dinitrogenases that utilize other metals as alternatives to Mo. Bishop and Premakumar [43] have established that vanadium-iron or iron-only dinitrogenases can function in place of Mo dinitrogenase. In the absence of Mo, the organisms can insert V into dinitrogenase instead of Mo the active site of the enzyme then is at FeVco rather than at FeMoco. Likewise, FeFeco can serve as the all-iron active site. 

Evidence for an alternative oxidative stress protection mechanism in sulfate-reducing bacteria has begun to emerge. Table 10.1 provides data on the proteins implicated in this alternative system. All but one of these proteins contain distinctive types of nonheme iron active sites. This chapter describes recent results on three of these novel proteins DcrH, Rbo, and Rbr, all from Desulfovibrio vulgaris HUdenborough. 

Scheme 2.6 Examples of reactions catalyzed byenzymesthat carry a dinudear iron active site (a) hydroxylation of methane by soluble methane monooxygenase (sMMO) [7] (b) reduction of ribonucleotides by class I ribonucleotide reductase (RNR)...

In 2002, an iron-activated nucleophilic aromatic substitution on a solid phase (resin-bound) was published by Ruhland et al. [89]. They demonstrated its first application by the synthesis of a library of o-, m- and p-heteroatom-substituted... 

Parameter Short-chain ADH Medium-chain ADH Long-chain ADH, iron-activated... 

The third subgroup of alcohol dehydrogenases consists of iron-activated enzymes. The first enzyme detected to belong to this group was the ADH II from Zymomonas mobilis [116] followed by the observation that the ADH IV from Saccharomyces cerevisiae shows more than 50% identity to this bacterial ADH [117]. No data about the secondary or tertiary structures of the enzymes in this subgroup are available currently. A prediction based upon the Chou and Fasman analysis [118] indicates that these enzymes are rich in a-helices. 

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