Iron-containing Enzymes Versatile Catalysts of Hydroxylation Reactions in Nature
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Contents:
Two important groups of mononuclear, non-heme iron dioxygenases are catechol dioxygenases and 2-oxoglutarate 2OG -dependent dioxygenases. Intradiol enzymes cleave the carbon-carbon bond between the two hydroxyl groups. The active ferric center is coordinated by four protein ligands—two histidine and two tyrosinate residues —in a trigonal bipyramidal manner with a water molecule occupying the fifth coordination site.
This then allows for reaction with dioxygen and subsequent intradiol cleavage to occur through a cyclic anhydride intermediate. Once a substrate binds to the ferrous center, this promotes dioxygen binding and subsequent activation. Bidentate coordination of 2OG and water completes a pseudo-octahedral coordination sphere.
- Stringency of the 2-His–1-Asp Active-Site Motif in Prolyl 4-Hydroxylase;
- Iron Proteins, Mononuclear (non-heme) Iron Oxygenases.
- The Trinity: An Interdisciplinary Symposium on the Trinity.
Following substrate binding, the water ligand is released, yielding an open coordination site for oxygen activation. This powerful oxidant is then utilized to carry out various reactions, including hydroxylation, halogenation, and demethylation.
Iron-Containing Enzymes
This radical then couples to the hydroxide ligand, producing the hydroxylated product and the Fe II resting state of the enzyme. The Rieske dioxygenases catalyze the cis-dihydroxylation of arenes to cis-dihydro-diol products. These enzymes are prominently found in soil bacteria such as Pseudomonas , [3] and their reactions constitute the initial step in aromatic hydrocarbon biodegradation. While this distance would appear optimal for efficient electron transfer, replacement of the bridging aspartate residue causes a loss of enzyme function, suggesting that electron transfer instead proceeds through the hydrogen-bonding network held in place by this aspartate residue.
The mechanistic picture for this class of dioxygenases is not yet clear, but there is evidence supporting an iron III hydroperoxy intermediate in the reaction pathway. While most iron-dependent dioxygenases utilize a non-heme iron cofactor, the oxidation of L- and D- tryptophan to N-formylkynurenine is catalyzed by either tryptophan 2,3-dioxygenase TDO or indoleamine 2,3-dioxygenase IDO , which are heme dioxygenases that utilize iron coordinated by a heme B prosthetic group. While iron is by far the most prevalent cofactor used for enzymatic dioxygenation, it is not required by all dioxygenases for catalysis.
Quercetin 2,3-dioxygenase quercetinase, QueD catalyzes the dioxygenolytic cleavage of quercetin to 2-protocatechuoylphloroglucinolcarboxylic acid and carbon monoxide. Acireductone 1,2-dihydroxy methylthio pentenone dioxygenase ARD is found in both prokaryotes and eukaryotes. However, ARD from Klebsiella oxytoca catalyzes an additional reaction when nickel II is bound: it instead produces 3- methylthio propionate, formate, and carbon monoxide from the reaction of acireductone with dioxygen. The activity of Fe-ARD is closely interwoven with the methionine salvage pathway, in which the methylthioadenosine product of cellular S-Adenosyl methionine SAM reactions is eventually converted to acireductone.
While the exact role of Ni-ARD is not known, it is suspected to help regulate methionine levels by acting as a shunt in the salvage pathway. This K.
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The quercetinases and ARD enzymes all are members of the cupin superfamily , to which the mononuclear iron enzymes also belong. In the ARD enzymes, the metal exists in an octahedral arrangement with the three histidine residues comprising a facial triad.
The ability of these dioxygenases to retain activity in the presence of other metal cofactors with wide ranges of redox potentials suggests the metal center does not play an active role in the activation of dioxygen. Rather, it is thought the metal center functions to hold the substrate in the proper geometry for it to react with dioxygen. In this respect, these enzymes are reminiscent of the intradiol catechol dioxygenases whereby the metal centers activate the substrate for subsequent reaction with dioxygen.
Dioxygenases that catalyze reactions without the need for a cofactor are much more rare in nature than those that do require them.
Biocatalysis Fueled by Light: On the Versatile Combination of Photocatalysis and Enzymes
Two dioxygenases, 1Hhydroxyoxo-quinoline 2,4-dioxygenase QDO and 1Hhydroxyoxoquinaldine 2,4-dioxygenase HDO , have been shown to require neither an organic or metal cofactor. Due to the degree of diversity in the dioxygenase family, dioxygenases have a wide range of influences in biology:.
- Book chapters.
- Philosophy after Marx: 100 Years of Misreadings and the Normative Turn in Political Philosophy (Historical Materialism Book Series, Volume 65).
- Man Everlasting.
- Non-heme Iron-Dependent Dioxygenases: Mechanism and Structure.
From Wikipedia, the free encyclopedia. Dioxygenase crystal structure of acinetobacter sp.
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Biochemical Society Transactions. Chemical Reviews. Iron-containing enzymes versatile catalysts of hydroxylation reactions in nature. Royal Society of Chemistry.
Ortiz de Montellano Ed. Kadish, K.
Smith, R. Guilard Eds. World Scientific Publishing Co. Kumar Eds. Faponle, M. Quesne, C. Sastri, F. Banse, S.