scholarly journals The role of porphyrin peripheral substituents in determining the reactivities of ferrous nitrosyl species

2020 ◽  
Vol 11 (23) ◽  
pp. 5909-5921
Author(s):  
Sk Amanullah ◽  
Abhishek Dey
Keyword(s):  
Nitrite Reductases ◽  
Catalytic Cycles

Ferrous nitrosyl {FeNO}7 species is an intermediate common to the catalytic cycles of Cd1NiR and CcNiR, two heme-based nitrite reductases (NiR), and its reactivity varies dramatically in these enzymes.

New insights into the activity of Pseudomonas aeruginosa cd1 nitrite reductase

2008 ◽  
Vol 36 (6) ◽  
pp. 1155-1159 ◽  
Author(s):  
Serena Rinaldo ◽  
Alessandro Arcovito ◽  
Giorgio Giardina ◽  
Nicoletta Castiglione ◽  
Maurizio Brunori ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Pseudomonas Aeruginosa ◽  
Nitrite Reductase ◽  
Nitrite Reduction ◽  
Nitrite Reductases ◽  
Cytochrome Cd1 ◽  
Haem Iron ◽  
Shed Light ◽  
Denitrification Process

The cytochrome cd1 nitrite reductases are enzymes that catalyse the reduction of nitrite to nitric oxide (NO) in the bacterial energy conversion denitrification process. These enzymes contain two different redox centres: one covalently bound c-haem, which is reduced by external donors, and one peculiar d1-haem, where catalysis occurs. In the present paper, we summarize the current understanding of the reaction of nitrite reduction in the light of the most recent results on the enzyme from Pseudomonas aeruginosa and discuss the differences between enzymes from different organisms. We have evidence that release of NO from the ferrous d1-haem occurs rapidly enough to be fully compatible with the turnover, in contrast with previous hypotheses, and that the substrate nitrite is able to displace NO from the d1-haem iron. These results shed light on the mechanistic details of the activity of cd1 nitrite reductases and on the biological role of the d1-haem, whose presence in this class of enzymes has to date been unexplained.

Cellular functions of ascorbic acid

1990 ◽  
Vol 68 (10) ◽  
pp. 1166-1173 ◽  
Author(s):  
Harish Padh
Keyword(s):  
Ascorbic Acid ◽  
Reduced Form ◽  
Enzymatic Reactions ◽  
Cellular Functions ◽  
Animal Cells ◽  
Major Function ◽  
Collagen Formation ◽  
Oxidative Products ◽  
Catalytic Cycles

It has long been suspected that ascorbic acid is involved in many cellular reactions. This is evident from the multitude of seemingly unrelated symptoms seen in scurvy. However, until recently, our understanding of its involvement was confined to its role in the synthesis of collagen. Studies in the past few years have unveiled mechanisms of its actions in collagen formation and many other enzymatic reactions. In addition, numerous physiological responses are reportedly affected by ascorbic acid. From the well-characterized enzymatic reactions involving ascorbic acid, it has become clear that in animal cells the ascorbate does not seem to be directly involved in catalytic cycles. Rather its major function seems to keep prosthetic metal ions in their reduced form. The role of ascorbate as a reductant in these enzymatic reactions complements its other antioxidant functions which have been recently appreciated, including that as a scavenger of free radicals. Therefore, it seems that the major function of ascorbate is to protect tissues from harmful oxidative products and to keep certain enzymes in their required reduced forms. However, it remains unclear how the deficiency of ascorbate leads to the pathological symptoms found in scurvy.Key words: ascorbic acid, vitamin C, biochemical functions, antioxidant, recommended dietary allowances, hydroxylation.

scholarly journals Dissecting the role of NtrC and RpoN in the expression of assimilatory nitrate and nitrite reductases in Bradyrhizobium diazoefficiens

2016 ◽  
Vol 110 (4) ◽  
pp. 531-542 ◽  
Author(s):  
María F. López ◽  
Juan J. Cabrera ◽  
Ana Salas ◽  
María J. Delgado ◽  
Silvina L. López-García
Keyword(s):  
Nitrite Reductases ◽  
Nitrate And Nitrite

The Peroxidase Reaction of Human Methaemoglobin: Character of the Amino Acid Electrondonor and the Influence of Oxygen

1993 ◽  
Vol 58 (11) ◽  
pp. 2715-2719
Author(s):  
Pavel Stopka ◽  
Zdeněk Pavlíček ◽  
Jana Lhotová
Keyword(s):  
Peroxidase Activity ◽  
Superoxide Anion ◽  
Anion Radical ◽  
High Probability ◽  
Esr Spectra ◽  
Superoxide Anion Radical ◽  
Peroxidase Reaction ◽  
Radical Content ◽  
Catalytic Cycles

The chemical modification of tyrosyl residues in methaemoglobin led to the decreased peroxidase activity and thus confirmed the role of tyrosyl residues in the catalytic process. The ESR spectra of methaemoglobin modified by tetranitromethane showed on the participation of tyrosine in the generation of superoxide anion radical. After repeated catalytic cycles the rapid decreasing of superoxide anion radical content was observed. This fact indicated, that the generation generation of superoxide anion radical is connected with tyrosyl residue. The residues with high probability are the source of the second electron in the peroxidase reaction the dissolved oxygen in the reaction mixture is necessary. This oxygen is also responsible for tyrosine destruction and thus for the decreasing of peroxidase activity of methaemoglobin.

Kinetics of CO binding and CO photodissociation in Pseudomonas stutzeri cd1 nitrite reductase: probing the role of extended N-termini in fast structural relaxation upon CO photodissociation

2001 ◽  
Vol 355 (1) ◽  
pp. 39-43 ◽  
Author(s):  
Emma K. WILSON ◽  
Andrea BELLELLI ◽  
Francesca CUTRUZZOLÀ ◽  
Walter G. ZUMFT ◽  
Aldo GUTIERREZ ◽  
...  
Keyword(s):  
Structural Relaxation ◽  
Nitrite Reductase ◽  
Pseudomonas Stutzeri ◽  
Intrinsic Property ◽  
Structural Reorganization ◽  
Nitrite Reductases ◽  
Intimate Association ◽  
Kinetics Of ◽  
Flow Experiments

cd 1 nitrite reductase from Pseudomonas stutzeri is a di-haem- containing enzyme, comprising a c-type haem and a d-type haem. Studies with the highly related cd1 nitrite reductase of Pseudomonas aeruginosahave established that this enzyme undergoes fast (microsecond) and global structural relaxation upon CO photodissociation from the reduced enzyme. A key difference between the Ps. aeruginosa and Ps. stutzerienzyme is the absence of a flexible N-terminal extension in the Ps. stutzeri enzyme. In Ps. aeruginosacd1 nitrite reductase the N-terminal extension wraps around the second subunit of the homodimer and with Tyr10 stabilizing a water molecule co-ordinated to the d1-haem. Given the intimate association of the N-terminal extension with the d1-haem, we hypothesized that the presence of the N-terminal extension likely contributes to the fast structural reorganization seen during photodissociation of CO from the reduced enzyme. In the present study we have investigated the kinetics of CO association and CO photodissociation of Ps. stutzericd1 nitrite reductase (which lacks the N-terminal arm seen in the Ps. aeruginosa enzyme) to probe the role and influence of the N-terminal arm in the fast global structural reorganization seen with Ps. aeruginosa. Surprisingly, we find that Ps. stutzericd1 nitrite reductase also undergoes fast structural reorganization during CO photodissociation. We also show, in stopped-flow experiments, that the kinetics of CO binding and dissociation with reduced Ps. stutzericd1 nitrite reductase are similar to those observed with Ps. aeruginosa enzyme, thus ruling out a major role for the N-terminal flexible arm found in Ps. aeruginosain the kinetics of these processes. Our data indicate that global structural reorganization following CO photodissociation is an intrinsic property of the haem domains in cd1 nitrite reductases. The absence of an N-terminal extension, as in the Ps. stutzericd1 nitrite reductase, does not lead to loss of global structural reorganization following CO photodissociation.

scholarly journals Structures of substrate- and product-bound forms of a multi-domain copper nitrite reductase shed light on the role of domain tethering in protein complexes

IUCrJ ◽  
2020 ◽  
Vol 7 (3) ◽  
pp. 557-565
Author(s):  
Daisuke Sasaki ◽  
Tatiana F. Watanabe ◽  
Robert R. Eady ◽  
Richard C. Garratt ◽  
Svetlana V. Antonyuk ◽  
...  
Keyword(s):  
Bound States ◽  
Protein Complexes ◽  
Conformational Search ◽  
Combined System ◽  
Nitrite Reductases ◽  
Protein Electron Transfer ◽  
C And N ◽  
Electron Transfer Complex ◽  
Global Nitrogen Cycle

Copper-containing nitrite reductases (CuNiRs) are found in all three kingdoms of life and play a major role in the denitrification branch of the global nitrogen cycle where nitrate is used in place of dioxygen as an electron acceptor in respiratory energy metabolism. Several C- and N-terminal redox domain tethered CuNiRs have been identified and structurally characterized during the last decade. Our understanding of the role of tethered domains in these new classes of three-domain CuNiRs, where an extra cytochrome or cupredoxin domain is tethered to the catalytic two-domain CuNiRs, has remained limited. This is further compounded by a complete lack of substrate-bound structures for these tethered CuNiRs. There is still no substrate-bound structure for any of the as-isolated wild-type tethered enzymes. Here, structures of nitrite and product-bound states from a nitrite-soaked crystal of the N-terminal cupredoxin-tethered enzyme from the Hyphomicrobium denitrificans strain 1NES1 (Hd 1NES1NiR) are provided. These, together with the as-isolated structure of the same species, provide clear evidence for the role of the N-terminal peptide bearing the conserved His27 in water-mediated anchoring of the substrate at the catalytic T2Cu site. Our data indicate a more complex role of tethering than the intuitive advantage for a partner-protein electron-transfer complex by narrowing the conformational search in such a combined system.

scholarly journals Nickel Nanoparticles Immobilized on a Porous Triazine-Thiourea-Sulfonamide as an Efficient Heterogeneous Catalyst for Reduction of Carbonyl Compounds

2021 ◽  
Author(s):  
Abumuslim Rahimi ◽  
Ramin Ghorbani-Vaghei ◽  
Sedigheh Alavinia
Keyword(s):  
Heterogeneous Catalyst ◽  
Nickel Nanoparticles ◽  
Low Cost ◽  
Polymer Support ◽  
Water As Solvent ◽  
Triethyl Amine ◽  
Silica Template ◽  
Catalytic Cycles

Abstract In order to investigate the role of silica template, polymers and nickel nanoparticles on the reduction of aldehydes/ketones, a novel porous triazine-thiourea-sulfonamide polymeric organic support (TTSA) was prepared via in-situ polymerization of melamine (1,3,5-triazine-2,4,6-triamine), thiourea and benzene-1,3-disulfonyl chloride in the presence of silica nanoparticles as a template led to the synthesize silica TTSA nanocomposite. Next, after removal of the template, the nanocomposite was transformed into mesoporous poly triazine-thiourea-sulfonamide. Ni nanoparticles (Ni NPs) were then decorated on the designed mesoporous polymer support and the resulting TTSA@Ni NPs nanospheres were employed as heterogeneous catalyst in the construction of alchohols from reduction of aldehydes/ketones using formic acid/triethyl amine as a reducing agent in water as solvent. The catalyst is low-cost, non-toxic, and can be reused for several catalytic cycles without decreasing the activity.

Reactions between iron porphyrins and tetrahydropterins

2004 ◽  
Vol 08 (03) ◽  
pp. 265-278 ◽  
Author(s):  
Daniel Mansuy ◽  
Delphine Mathieu ◽  
Pierrette Battioni ◽  
Jean-Luc Boucher
Keyword(s):  
Radical Reaction ◽  
Intermediate Formation ◽  
Redox Potentials ◽  
Iron Porphyrins ◽  
General Reaction ◽  
Cytochromes C ◽  
The One ◽  
Catalytic Cycles ◽  
Electron Transfers

Data from the last few years have revealed a novel biological role of the tetrahydrobiopterin ( H 4 B ) cofactor, in one-electron transfers to the heme of the active site of NO-synthases (NOSs) with intermediate formation of a H 4 B -derived radical. These electron transfers play a key role in the catalytic cycles of the two steps catalyzed by NOS, the N ω-hydroxylation of L-arginine, and the three-electron oxidation of N ω-hydroxyarginine to L-citrulline and NO. Recent experiments performed between various tetrahydropterins and iron porphyrins have shown that the one-electron transfer from tetrahydropterins, such as the natural cofactors H 4 B and tetrahydrofolate or the synthetic 6,7-dimethyltetrahydropterin (diMeH4P), to Fe(III) porphyrins of sufficiently high redox potentials (> about -100 mV versus NHE for the Fe(III)/Fe(II) couple) is a very general reaction that occurs with formation of a tetrahydropterin-derived radical. Reaction of diMeH4P with a stable porphyrin Fe(II)-O 2 complex leads to a diMeH4P-derived radical and a transient Fe(III)-OOH complex, mimicking the reaction between H 4 B and heme Fe(II)-O 2 in the NOS catalytic cycle. Tetrahydropterins such as diMeH4P also reduce hemeproteins Fe(III) of sufficiently high redox potentials, such as cytochromes c and b5 or metmyoglobin, to the corresponding hemeproteins Fe(II) .

The Role of Siroheme in Sulfite and Nitrite Reductases

Tetrapyrroles ◽  
2009 ◽  
pp. 375-389 ◽  
Author(s):  
M. Elizabeth Stroupe ◽  
Elizabeth D. Getzoff
Keyword(s):  
Nitrite Reductases
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