Nature's nitrite-to-ammonia expressway, with no stop at dinitrogen.

Since the characterization of cytochrome c as a multiheme nitrite reductase, research on this enzyme has gained major interest. Today, it is known as pentaheme cytochrome c nitrite reductase (NrfA). Part of the NH produced from NO is released as NH leading to nitrogen loss, similar to denitrification which generates NO, NO, and N.

A [3Cu:2S] cluster provides insight into the assembly and function of the Cu site of nitrous oxide reductase.

Nitrous oxide reductase (NOR) is the only known enzyme reducing environmentally critical nitrous oxide (NO) to dinitrogen (N) as the final step of bacterial denitrification. The assembly process of its unique catalytic [4Cu:2S] cluster Cu remains scarcely understood. Here we report on a mutagenesis study of all seven histidine ligands coordinating this copper center, followed by spectroscopic and structural characterization and based on an established, functional expression system for NOR in .

Histidine-Gated Proton-Coupled Electron Transfer to the Cu Site of Nitrous Oxide Reductase.

Copper-containing nitrous oxide reductase (NOR) is the only known enzyme to catalyze the conversion of the environmentally critical greenhouse gas nitrous oxide (NO) to dinitrogen (N) as the final step of bacterial denitrification. Other than its unique tetranuclear active site Cu, the binuclear electron entry point Cu is also utilized in other enzymes, including cytochrome oxidase. In the Cu site of NOR, a histidine ligand was found to undergo a conformational flip upon binding of the substrate NO between the two copper centers.

Cytochrome P450. The Dioxygen-Activating Heme Thiolate.

Cytochromes P450 (CYPs) are heme b-binding enzymes and belong to Nature's most versatile catalysts. They participate in countless essential life processes, and exist in all domains of life, Bacteria, Archaea, and Eukarya, and in viruses. CYPs attract the interest of researchers active in fields as diverse as biochemistry, chemistry, biophysics, molecular biology, pharmacology, and toxicology.

Sulfur, the Versatile Non-metal.

The non-metallic chemical element sulfur, 3216S , referred to in Genesis as brimstone and identified as element by Lavoisier, is the tenth most abundant element in the universe and the fifth most common element on Earth. Important inorganic forms of sulfur in the biosphere are elemental sulfur (S8), sulfate (SO2-4), and sulfide (S2-), sulfite (SO2-3), thiosulfate, (S2O23), and polythionates (S3O62-; S4O62-). Because of its wide range of stable oxidation states, from +6to -2, sulfur plays important roles in central biochemistry as a structural and redoxactive element and is intimately related to life on Earth.

Introduction: Transition Metals and Sulfur.

The number of transition metal ions which are essential to life - also often called trace elements - increased steadily over the years. In parallel, the list of biological functions in which transition metals are involved, has grown, and is still growing tremendously. Significant progress has been made in understanding the chemistry operating at the biological sites where metal ions have been discovered.

Walking the seven lines: binuclear copper A in cytochrome c oxidase and nitrous oxide reductase.

The enzymes nitrous oxide reductase (N2OR) and cytochrome c oxidase (COX) are constituents of important biological processes. N2OR is the terminal reductase in a respiratory chain converting NO to N in denitrifying bacteria; COX is the terminal oxidase of the aerobic respiratory chain of certain bacteria and eukaryotic organisms transforming O to HO accompanied by proton pumping. Different spectroscopies including magnetic resonance techniques, were applied to show that N2OR has a mixed-valent Cys-bridged [Cu(CyS)Cu] copper site, and that such a binuclear center, called CuA, does also exist in COX.

Anaerobic Microbial Degradation of Hydrocarbons: From Enzymatic Reactions to the Environment.

Hydrocarbons are abundant in anoxic environments and pose biochemical challenges to their anaerobic degradation by microorganisms. Within the framework of the Priority Program 1319, investigations funded by the Deutsche Forschungsgemeinschaft on the anaerobic microbial degradation of hydrocarbons ranged from isolation and enrichment of hitherto unknown hydrocarbon-degrading anaerobic microorganisms, discovery of novel reactions, detailed studies of enzyme mechanisms and structures to process-oriented in situ studies. Selected highlights from this program are collected in this synopsis, with more detailed information provided by theme-focused reviews of the special topic issue on 'Anaerobic biodegradation of hydrocarbons' [this issue, pp.

Structure and Function of the Unusual Tungsten Enzymes Acetylene Hydratase and Class II Benzoyl-Coenzyme A Reductase.

In biology, tungsten (W) is exclusively found in microbial enzymes bound to a bis-pyranopterin cofactor (bis-WPT). Previously known W enzymes catalyze redox oxo/hydroxyl transfer reactions by directly coordinating their substrates or products to the metal. They comprise the W-containing formate/formylmethanofuran dehydrogenases belonging to the dimethyl sulfoxide reductase (DMSOR) family and the aldehyde:ferredoxin oxidoreductase (AOR) families, which form a separate enzyme family within the Mo/W enzymes.

Acetylene hydratase: a non-redox enzyme with tungsten and iron-sulfur centers at the active site.

In living systems, tungsten is exclusively found in microbial enzymes coordinated by the pyranopterin cofactor, with additional metal coordination provided by oxygen and/or sulfur, and/or selenium atoms in diverse arrangements. Prominent examples are formate dehydrogenase, formylmethanofuran dehydrogenase, and aldehyde oxidoreductase all of which catalyze redox reactions. The bacterial enzyme acetylene hydratase (AH) stands out of its class as it catalyzes the conversion of acetylene to acetaldehyde, clearly a non-redox reaction and a reaction distinct from the reduction of acetylene to ethylene by nitrogenase.

The magic of dioxygen.

Oxygen has to be considered one of the most important elements on Earth. Earlier, some dispute arose as to which of the three scientists, Carl Wilhelm Scheele (Sweden), Joseph Priestley (United Kingdom) or Antoine Lavoisier (France), should get credit for the air of life.Today it is agreed that the Swede discovered it first, the fire air in 1772.

The role of molecular oxygen in the iron(III)-promoted oxidative dehydrogenation of amines.

A mechanistic study is presented of the oxidative dehydrogenation of the iron(III) complex [Fe(III)L(3)](3+), 1, (L(3) = 1,9-bis(2'-pyridyl)-5-[(ethoxy-2''-pyridyl)methyl]-2,5,8-triazanonane) in ethanol in the presence of molecular oxygen. The product of the reaction was identified by NMR spectroscopy and X-ray crystallography as the identical monoimine complex [Fe(II)L(4)](2+), 2, (L(4) = 1,9-bis(2'-pyridyl)-5-[(ethoxy-2''-pyridyl)methyl]-2,5,8-triazanon-1-ene) also formed under an inert nitrogen atmosphere. Molecular oxygen is an active player in the oxidative dehydrogenation of iron(III) complex 1.

The oxidative fermentation of ethanol in Gluconacetobacter diazotrophicus is a two-step pathway catalyzed by a single enzyme: alcohol-aldehyde Dehydrogenase (ADHa).

Gluconacetobacter diazotrophicus is a N2-fixing bacterium endophyte from sugar cane. The oxidation of ethanol to acetic acid of this organism takes place in the periplasmic space, and this reaction is catalyzed by two membrane-bound enzymes complexes: the alcohol dehydrogenase (ADH) and the aldehyde dehydrogenase (ALDH). We present strong evidence showing that the well-known membrane-bound Alcohol dehydrogenase (ADHa) of Ga.

The production of ammonia by multiheme cytochromes C.

The global biogeochemical nitrogen cycle is essential for life on Earth. Many of the underlying biotic reactions are catalyzed by a multitude of prokaryotic and eukaryotic life forms whereas others are exclusively carried out by microorganisms. The last century has seen the rise of a dramatic imbalance in the global nitrogen cycle due to human behavior that was mainly caused by the invention of the Haber-Bosch process.

Catalytic scope of the thiamine-dependent multifunctional enzyme cyclohexane-1,2-dione hydrolase.

The thiamine diphosphate (ThDP)-dependent enzyme cyclohexane-1,2-dione hydrolase (CDH) was expressed in Escherichia coli and purified by affinity chromatography (Ni-NTA). Recombinant CDH showed the same C-C bond-cleavage and C-C bond-formation activities as the native enzyme. Furthermore, we have shown that CDH catalyzes the asymmetric cross-benzoin reaction of aromatic aldehydes and (decarboxylated) pyruvate (up to quantitative conversion, 92-99 % ee).

Toxicity and deficiency of copper in Elsholtzia splendens affect photosynthesis biophysics, pigments and metal accumulation.

Elsholtzia splendens is a copper-tolerant plant species growing on copper deposits in China. Spatially and spectrally resolved kinetics of in vivo absorbance and chlorophyll fluorescence in mesophyll of E. splendens were used to investigate the copper-induced stress from deficiency and toxicity as well as the acclimation to excess copper stress.

In vivo speciation studies and antioxidant properties of bromine in Laminaria digitata reinforce the significance of iodine accumulation for kelps.

The metabolism of bromine in marine brown algae remains poorly understood. This contrasts with the recent finding that the accumulation of iodide in the brown alga Laminaria serves the provision of an inorganic antioxidant - the first case documented from a living system. The aim of this study was to use an interdisciplinary array of techniques to study the chemical speciation, transformation, and function of bromine in Laminaria and to investigate the link between bromine and iodine metabolism, in particular in the antioxidant context.

Microbial sulfite respiration.

Despite its reactivity and hence toxicity to living cells, sulfite is readily converted by various microorganisms using distinct assimilatory and dissimilatory metabolic routes. In respiratory pathways, sulfite either serves as a primary electron donor or terminal electron acceptor (yielding sulfate or sulfide, respectively), and its conversion drives electron transport chains that are coupled to chemiosmotic ATP synthesis. Notably, such processes are also seen to play a general role in sulfite detoxification, which is assumed to have an evolutionary ancient origin.

Conserving energy with sulfate around 100 °C--structure and mechanism of key metal enzymes in hyperthermophilic Archaeoglobus fulgidus.

Sulfate-reducing bacteria and archaea are important players in the biogeochemical sulfur cycle. ATP sulfurylase, adenosine 5'-phosphosulfate reductase and dissimilatory sulfite reductase are the key enzymes in the energy conserving process of SO4(2-) → H2S reduction. This review summarizes recent advances in our understanding of the activation of sulfate to adenosine 5'-phosphosulfate, the following reductive cleavage to SO3(2-) and AMP, and the final six-electron reduction of SO3(2-) to H2S in the hyperthermophilic archaeon Archaeoglobus fulgidus.

Nature's way of handling a greenhouse gas: the copper-sulfur cluster of purple nitrous oxide reductase.

The tetranuclear Cu(Z) cluster is the unique active site of nitrous oxide reductase, the enzyme that catalyzes the reduction of nitrous oxide to dinitrogen as the final reaction in bacterial denitrification. Three-dimensional structures of orthologs of the enzyme from a variety of different bacterial species were essential steps in the elucidation of the properties of this center. However, while structural data first revealed and later confirmed the presence of four copper ions in spectroscopically distinct forms of Cu(Z), the exact structure and stoichiometry of the cluster showed significant variations.

The catalytic redox activity of prion protein-Cu(II) is controlled by metal exchange with the Zn(II) -thiolate clusters of Zn(7) metallothionein-3.

Silencing prion: Copper-catalyzed transformations of prion protein (PrP) lead to the production of reactive oxygen species (ROS), PrP oxidation, and cleavage and aggregation in transmissible spongiphorm encephalopathies. Zn(7) MT-3 efficiently targets Cu(II) bound in different coordination modes to PrP-Cu(II) . By an unusual redox-dependent metal-swap reaction, MT-3 modulates the catalytic redox properties of PrP-Cu(II) .

Crystal structure of a ring-cleaving cyclohexane-1,2-dione hydrolase, a novel member of the thiamine diphosphate enzyme family.

The thiamine diphosphate (ThDP) dependent flavoenzyme cyclohexane-1,2-dione hydrolase (CDH) (EC 3.7.1.