Influence of Cysteine 440 on the Active Site Properties of 3-Deoxy-d-Arabino-Heptulosonate 7-Phosphate Synthase in (DAHPS).

The shikimate pathway, which produces aromatic amino acids and key intermediates, is critical to the viability of the tuberculosis-causing pathogen . The enzyme 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (DAHPS) catalyzes the first committed step of this pathway and possesses regulatory functions. Its active site contains two cysteinyls: one (Cys) bound to a metal ion, while the other (Cys) is in proximity to the first but is located on a connecting loop.

Mechanism of substrate inhibition in cytochrome-c dependent NO reductases from denitrifying bacteria (cNORs).

Steady-state kinetics of cytochrome-c dependent denitrifying NO reductases (cNORs) show evidence of substrate inhibition at NO concentrations higher than 10 μM, but the mechanism of inhibition remains unclear. Here, we present low-temperature FTIR photolysis experiments carried out on the NO complex formed by addition of NO to the oxidized cNORs. A differential signal at 1261 cm that downshifts with NO and NO is assigned to a ν(NO) from a bridging diiron-nitrito complex at the heme-nonheme diron site.

Molecular Dynamics Simulations of a Cytochrome P450 from (P450-TT) Reveal How Its Substrate-Binding Channel Opens.

Cytochrome P450s (P450) are important enzymes in biology with useful biochemical reactions in, for instance, drug and xenobiotics metabolisms, biotechnology, and health. Recently, the crystal structure of a new member of the CYP116B family has been resolved. This enzyme is a cytochrome P450 (CYP116B46) from (P450-TT) and has potential for the oxy-functionalization of organic molecules such as fatty acids, terpenes, steroids, and statins.

How external perturbations affect the chemoselectivity of substrate activation by cytochrome P450 OleT.

Cytochrome P450 enzymes are versatile biocatalysts found in most forms of life. Generally, the cytochrome P450s react with dioxygen and hence are haem-based mono-oxygenases; however, in specific isozymes, H2O2 rather than O2 is used and these P450s act as peroxygenases. The P450 OleTJE is a peroxygenase that binds long to medium chain fatty acids and converts them to a range of products originating from Cα-hydroxylation, Cβ-hydroxylation, Cα-Cβ desaturation and decarboxylation of the substrate.

Recombinant silicateins as model biocatalysts in organosiloxane chemistry.

The family of silicatein enzymes from marine sponges (phylum Porifera) is unique in nature for catalyzing the formation of inorganic silica structures, which the organisms incorporate into their skeleton. However, the synthesis of organosiloxanes catalyzed by these enzymes has thus far remained largely unexplored. To investigate the reactivity of these enzymes in relation to this important class of compounds, their catalysis of Si-O bond hydrolysis and condensation was investigated with a range of model organosilanols and silyl ethers.

Sulfoxide Synthase versus Cysteine Dioxygenase Reactivity in a Nonheme Iron Enzyme.

The sulfoxide synthase EgtB represents a unique family of nonheme iron enzymes that catalyze the formation of a C-S bond between N-α-trimethyl histidine and γ-glutamyl cysteine, which is the key step in the biosynthesis of ergothioneine, an important amino acid related to aging. A controversy has arisen regarding its catalytic mechanism related to the function of the active-site Tyr residue. The biosynthesis of ergothioneine in EgtB shows structural similarities to cysteine dioxygenase which transfers two oxygen atoms to the thiolate group of cysteine.

A High-Valent Non-Heme μ-Oxo Manganese(IV) Dimer Generated from a Thiolate-Bound Manganese(II) Complex and Dioxygen.

This study deals with the unprecedented reactivity of dinuclear non-heme Mn -thiolate complexes with O , which dependent on the protonation state of the initial Mn dimer selectively generates either a di-μ-oxo or μ-oxo-μ-hydroxo Mn complex. Both dimers have been characterized by different techniques including single-crystal X-ray diffraction and mass spectrometry. Oxygenation reactions carried out with labeled O unambiguously show that the oxygen atoms present in the Mn dimers originate from O .

Glutathione binding to dirhodium tetraacetate: a spectroscopic, mass spectral and computational study of an anti-tumour compound.

Glutathione (γ-l-glutamyl-l-cysteinyl-glycine) is a ubiquitous tripeptide found in all plants and animals. Glutathione has key roles as a metallochaperone and as a cellular thiol involved in metabolism. Little is known about how glutathione interacts with organometallic compounds in vivo.

Reactivity Patterns of (Protonated) Compound II and Compound I of Cytochrome P450: Which is the Better Oxidant?

The cytochromes P450 are versatile enzymes in human physiology that perform substrate hydroxylation reactions extremely efficiently. In this work, we present results of a computational study on the reactivity patterns of Compound I, Compound II, and protonated Compound II with model substrates, and we address the question of which of these compounds is the most effective oxidant? All calculations, regardless of the substrate, implicated that Compound I is the superior oxidant of the three. However, Compound II and protonated Compound II were found to react with free energies of activation that are only a few kcal mol higher in energy than those obtained with Compound I.

Substrate Sulfoxidation by an Iron(IV)-Oxo Complex: Benchmarking Computationally Calculated Barrier Heights to Experiment.

High-valent metal-oxo oxidants are common reactive species in synthetic catalysts as well as heme and nonheme iron enzymes. In general, they efficiently react with substrates through oxygen atom transfer, and for a number of cases, experimental rate constants have been determined. However, because these rate constants are generally measured in a polar solution, it has been found difficult to find computational methodologies to reproduce experimental trends and reactivities.

Influence of Ligand Architecture in Tuning Reaction Bifurcation Pathways for Chlorite Oxidation by Non-Heme Iron Complexes.

Reaction bifurcation processes are often encountered in the oxidation of substrates by enzymes and generally lead to a mixture of products. One particular bifurcation process that is common in biology relates to electron transfer versus oxygen atom transfer by high-valent iron(IV)-oxo complexes, which nature uses for the oxidation of metabolites and drugs. In biomimicry and bioremediation, an important reaction relates to the detoxification of ClO in water, which can lead to a mixture of products through bifurcated reactions.

Deformylation Reaction by a Nonheme Manganese(III)-Peroxo Complex via Initial Hydrogen-Atom Abstraction.

Metal-peroxo intermediates are key species in the catalytic cycles of nonheme metalloenzymes, but their chemical properties and reactivity patterns are still poorly understood. The synthesis and characterization of a manganese(III)-peroxo complex with a pentadentate bispidine ligand system and its reactivity with aldehydes was studied. Manganese(III)-peroxo can react through hydrogen-atom abstraction reactions instead of the commonly proposed nucleophilic addition reaction.

Influence of cysteine 164 on active site structure in rat cysteine dioxygenase.

Cysteine dioxygenase is a non-heme mononuclear iron enzyme with unique structural features, namely an intramolecular thioether cross-link between cysteine 93 and tyrosine 157, and a disulfide bond between substrate L-cysteine and cysteine 164 in the entrance channel to the active site. We investigated how these posttranslational modifications affect catalysis through a kinetic, crystallographic and computational study. The enzyme kinetics of a C164S variant are identical to WT, indicating that disulfide formation at C164 does not significantly impair access to the active site at physiological pH.

Arene activation by a nonheme iron(III)-hydroperoxo complex: pathways leading to phenol and ketone products.

Iron(III)-hydroperoxo complexes are found in various nonheme iron enzymes as catalytic cycle intermediates; however, little is known on their catalytic properties. The recent work of Banse and co-workers on a biomimetic nonheme iron(III)-hydroperoxo complex provided evidence of its involvement in reactivity with arenes. This contrasts the behavior of heme iron(III)-hydroperoxo complexes that are known to be sluggish oxidants.

Origin of the Regioselective Fatty-Acid Hydroxylation versus Decarboxylation by a Cytochrome P450 Peroxygenase: What Drives the Reaction to Biofuel Production?

The cytochromes P450 are heme-based mono-oxygenases or peroxygenases involved in vital reaction processes for human health. A recently described P450 per-oxygenase, OleTJE , converts long-chain fatty acids to terminal olefins and as such may have biotechnological relevance in biodiesel production. However, the reaction produces significant amounts of α- and β-hydroxylation by-products, and their origin are poorly understood.

Site-selective formation of an iron(iv)-oxo species at the more electron-rich iron atom of heteroleptic μ-nitrido diiron phthalocyanines.

Iron(iv)-oxo species have been identified as the active intermediates in key enzymatic processes, and their catalytic properties are strongly affected by the equatorial and axial ligands bound to the metal, but details of these effects are still unresolved. In our aim to create better and more efficient oxidants of H-atom abstraction reactions, we have investigated a unique heteroleptic diiron phthalocyanine complex. We propose a novel intramolecular approach to determine the structural features that govern the catalytic activity of iron(iv)-oxo sites.

Drug metabolism by cytochrome p450 enzymes: what distinguishes the pathways leading to substrate hydroxylation over desaturation?

Cytochrome P450 enzymes are highly versatile biological catalysts in our body that react with a broad range of substrates. Key functions in the liver include the metabolism of drugs and xenobiotics. One particular metabolic pathway that is poorly understood relates to the P450 activation of aliphatic groups leading to either hydroxylation or desaturation pathways.

Differences and comparisons of the properties and reactivities of iron(III)-hydroperoxo complexes with saturated coordination sphere.

Heme and nonheme monoxygenases and dioxygenases catalyze important oxygen atom transfer reactions to substrates in the body. It is now well established that the cytochrome P450 enzymes react through the formation of a high-valent iron(IV)-oxo heme cation radical. Its precursor in the catalytic cycle, the iron(III)-hydroperoxo complex, was tested for catalytic activity and found to be a sluggish oxidant of hydroxylation, epoxidation and sulfoxidation reactions.

Long-range electron transfer triggers mechanistic differences between iron(IV)-oxo and iron(IV)-imido oxidants.

Nature often utilizes molecular oxygen for oxidation reactions through monoxygenases and dioxygenases. In many of these systems, a high-valent iron(IV)-oxo active species is found. In recent years, evidence has accumulated of possible iron(IV)-imido and iron(V)-nitrido intermediates in enzymatic catalysis, although little is known about their activity.