Enzyme-catalyzed dioxygenation

Copper(II) complexes with phenoxo ligands have attracted great interest, in order to develop basic coordination chemistry for their possible use as models for tyrosinase activity (dimeric complexes) and fungal enzyme galactose oxidase (GO) (monomeric complexes). The latter enzyme catalyzes the two-electron oxidation of primary alcohols with dioxygen to yield aldehyde and... 

Monooxygenase enzymes catalyze reactions in which one atom of oxygen derived from dioxygen is incorporated into an organic substrate while the other atom is reduced by two electrons to form water (1,2). 

This enzyme catalyzes the NADPH- and dioxygen-dependent insertion of cis double bonds into the methylene region of fatty acyl structures covalently attached to the phosphopantetheine portion of an acyl carrier protein. 

This group of enzymes catalyzes the oxidation of amines. Amine oxidase [EC 1.4.3.4], a flavin-containing enzyme (also known as monoamine oxidase, tyramine oxidase, tyraminase, or adrenalin oxidase) catalyzes the reaction of an organic amine R—CH2—NH2) with dioxygen... 

Peroxidase and catalase enzymes catalyze oxidations by hydrogen peroxide and the disproportionation of hydrogen peroxide into dioxygen and water (equations 36 and 37). The two classes of... 

Ascorbate oxidase, laccase, and ceruloplasmin form the group of blue oxidases. These are multicopper enzymes catalyzing the four-electron reduction of dioxygen to water with concomitant one-electron oxidation of the substrate (3), which is very similar to the reaction performed by cytochrome c oxidase. All three enzymes have been known for many years, and an overwhelming number of papers have appeared since their discovery dealing with the different aspects of these enzymes. 

Iron can be said to be the most chemically versatile of all the elements used by nature. It is essential for dioxygen uptake and transport in the vast majority of living systems, is ubiquitous in electron transfer relays and oxygen metabolism, is used widely as the catalytic center in enzymes catalyzing chemical changes as diverse as dinitrogen fixation, nitrate reduction, and isopenicillin-N-synthase, and is vital for DNA... 

The aliphatic alcohol oxidase, a FAD-dependent enzyme, catalyzes the oxidation of primary short-chain alcohols to the corresponding aldehydes. Dioxygen can be replaced by synthetic acceptors such as dichlorophenolindophenol or phenazine methosulfate [147l... 

Jefford, C. W., and P. A. Cadby. Molecular mechanisms of enzyme-catalyzed dioxygenation. 

Manganese superoxide dismutase (MnSOD) is a redox-active manganese enzyme that employs a mononuclear manganese ion at its active site. Discovered in 1970 (52), this enzyme catalyzes the dismuta-tion of superoxide (H02), to dioxygen and hydrogen peroxide, as shown in Scheme 2. Superoxide is the radical, one-electron-reduced... 

Monooxygenases represent a class of enzymes catalyzing a reductive activation of dioxygen, linked to the insertion of an oxygen atom into a C-H bond according to Equation (6). 

Besides dioxygen, nitrogen oxides can serve as electron acceptors in reactions catalyzed by copper enzymes. The copper-containing nitrite reductase (NIR) from denitrifying bacteria such as Achromobaaer, Pseudomonas, or Rhodobacter is part of the dissimilatory metabolic pathway of these bacteria. The enzyme catalyzes the one-electron reduction of NO2 to NO and water according to Equations (14) and (15). 

Prolyl hydroxylase was the first a-ketoglutarate-dependent dioxygenase to be identified, in 1967, by Udenfriend. This enzyme catalyzes the hydroxylation of prolyl residues in collagen to 4-hydroxy-prolyl residues (Figure 32). One oxygen atom is incorporated from dioxygen into the hydroxylated product, and one... 

Finally, as shown in Table V, activity of ferrochelatase is also decreased by -NO. This mitochondrial enzyme catalyzes the final step in heme synthesis, the insertion of ferrous iron into porphyrin, and has been shown to contain an Fc2S2 nonheme iron-sulfur cluster which is required for activity (Dailey et aL, 1994). This result suggests that loss of activity may occur by nitrogen oxide-mediated [i.e., -NO in the presence of dioxygen (Wink et aL, 1993a)] destruction of its iron-sulfur cluster. Consistent with this result, while inhibition of ALAS and increase in HO induced by SNAP requires a period of 4-8 hr (consistent with the established effects of heme on these enzymes, as described above), the inhibition of ferrochelatase is virtually complete within 1 hr (Kim et aL, 1995). 

Some enzymes capable of oxidizing C-H bonds contain copper ions [52]. For example, tyrosinase [53a] contains a coupled, binuclear copper active site which reversibly binds dioxygen as a peroxide that bridges between the two copper ions. This enzyme catalyzes the orthohydroxylation of phenols with further oxidation of catechol to an ortho-quimne [53b-d], The mechanism proposed for phenolase activity of tyrosinase is shown in Scheme XI. 13 [521]. 

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