Nonheme iron-dependent monooxygenases

Nonheme iron-dependent monooxygenases, which use two iron atoms as cofactors, are bacterial multicomponent monooxygenases. They mainly consist of three components, including a monooxygenase, a reductase component, and a small regulatory... 

Although many nonheme iron-dependent monooxygenases have been purified and cloned from hydrocarbon-utilizing bacteria, the complicated nature of this enzyme family often places a considerable synthetic burden on the host cells during heterologous expression. Therefore, the whole cells of the native strains or recombinant E. coli, instead of free enzymes, are often applied in biocatalytic reactions. 

Reactions Catalyzed with Nonheme Iron-Dependent Monooxygenases... 

Microorganisms that use gaseous olefins as a carbon source are widely exist in nature, and they typically produce nonheme iron-dependent alkene/alkane monooxygenases. Although in a lot of cases, the identification of the key enzyme hasn t been attempted many of those alkene-utilizing bacteria have been used in the asymmetric epoxidation of aliphatic alkenes with high stereoselectivities [26]. 

Other non-heme enzymes that use dioxygen are 4-methoxy-benzoate O-demethylase, extradiol catechol dioxygenases, the oxidoreductase isopenicillin N synthase, and a-keto acid-dependent enzymes (28). Moreover, the BH4-dependent glyceryl-ether monooxygenase (GEM) also appears to be dependent on nonheme iron for catalysis (see also Section I.E). 

Figure 3 Activation of O2 by 2-oxo-glutarate dependent nonheme iron monooxygenases...

To date, no functional model systems have been developed to probe the reaetivity and structural characteristics of the family of aromatic nonheme iron tetrahydropterin-dependent monooxygenases. Currently, all mechanistic information regarding the reaetion pathways involved in PAH has been derived from in vitro studies on the protein. For a more detailed description of the evidence, the reader is directed to the aeeompanying referenees eited above. 

Important nonheme iron monooxygenases other than sMMO are pterin-dependent enzymes and isopenicillin N synthase. Three enzymes are known as the pterin-dependent monooxygenases phenylalanine hydroxylase (PAH), tyrosine hydroxylase (TH), and tryptophan hydroxylase (TPH). These enzymes perform metabolically important transformations, e,g, for the biosynthesis of neurotransmitters, and catalyze the reactions shown in Fig. 8. 

Recent remarkable progress in the clarification of the mechanisms of nonheme iron and copper monooxygenases depends on the X-ray crystallographic and other spectroscopic... 

In contrast, a coordinatively unsaturated a-ketoglutarate ferrous complex Fe(II)(BF)(HB-3,5-Me2pz)3 was reported very recently [90]. The dioxygen oxidation of this ferrous complex forms a reactive species capable of epoxidizing olefin. The reaction mechanism of this system has not yet been elucidated, while the reactivity of this system is markedly high and is expected to be a clue in understanding the mechanism of a-keto acid dependent nonheme iron monooxygenase. 

---