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Related Concept Videos

Inorganic Nitrogen Assimilation01:22

Inorganic Nitrogen Assimilation

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Nitrogen is an essential element in biological systems, forming a crucial component of proteins, nucleic acids, and other cellular constituents. Many bacteria and archaea acquire nitrogen in the form of nitrate (NO₃⁻) or ammonia (NH₃), which are then assimilated into biomolecules through specific enzymatic pathways.Assimilatory Nitrate ReductionWhen nitrate enters the cell, it undergoes a two-step reduction process known as assimilatory nitrate reduction. Initially, the enzyme...
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Redox Reactions01:27

Redox Reactions

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Redox reactions are vital biochemical processes that underpin energy metabolism in cells. These reactions involve the transfer of electrons between molecules, occurring in tandem as oxidation and reduction. Oxidation refers to the loss of electrons, while reduction denotes their gain. This coupling ensures the seamless flow of electrons through metabolic pathways. For example, in bacterial metabolism, glucose undergoes oxidation to carbon dioxide, while oxygen is simultaneously reduced to...
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2° Amines to N-Nitrosamines: Reaction with NaNO201:20

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Secondary amines react with nitrous acid to form N-nitrosamines, as depicted in Figure 1. Nitrous acid, a weak and unstable acid, is formed in situ from an aqueous solution of sodium nitrite and strong acids, such as hydrochloric acid or sulfuric acid, in cold conditions. In the presence of an acid, the nitrous acid gets protonated. The subsequent loss of water results in the formation of the electrophile known as nitrosonium ion.
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Electron Transport Chain: Complex I and II01:46

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The mitochondrial electron transport chain (ETC) is the main energy generation system in the eukaryotic cells. However, mitochondria also produce cytotoxic reactive oxygen species (ROS) due to the large electron flow during oxidative phosphorylation. While Complex I is one of the primary sources of superoxide radicals, ROS production by Complex II is uncommon and may only be observed in cancer cells with mutated complexes.
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Oximes can be reduced to primary amines using catalytic hydrogenation, hydride reduction, or sodium metal reduction. The reduction of aliphatic and aromatic nitro compounds to primary amines takes place by either catalytic hydrogenation or by using active metals like Fe, Zn, and Sn in the presence of an acid.
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The nitration of benzene is an example of an electrophilic aromatic substitution reaction. It involves the formation of a very powerful electrophile, the nitronium ion, which is linear in shape. The reaction occurs through the interaction of two strong acids, sulfuric and nitric acid.
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Nitrite Reductase Activity of Ferrous Nitrobindins: A Comparative Study.

Giovanna De Simone1, Alessandra di Masi1, Grazia R Tundo2

  • 1Dipartimento di Scienze, Università Roma Tre, 00146 Roma, Italy.

International Journal of Molecular Sciences
|April 13, 2023
PubMed
Summary

Nitrobindins (Nbs) are heme proteins that metabolize nitric oxide (NO). This study reveals their nitrite reductase activity, crucial for NO production and blood pressure regulation, particularly in tissues like the retina.

Keywords:
Arabidopsis thaliana nitrobindinDanio rerio nitrobindinHomo sapiens nitrobindinMycobacterium tuberculosis nitrobindinkineticsnitrite reductase activity

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Area of Science:

  • Biochemistry
  • Protein Science
  • Physiology

Background:

  • Nitrobindins (Nbs) are all-β-barrel heme proteins found across species, involved in reactive nitrogen species inactivation.
  • Nbs sequester nitric oxide (NO), convert NO to nitrous acid (HNO2), and isomerize peroxynitrite to nitrate (NO3-).

Purpose of the Study:

  • To investigate the nitrite reductase activity of Nitrobindins (II) from various species, including Mycobacterium tuberculosis, Arabidopsis thaliana, Danio rerio, and Homo sapiens.
  • To explore the role of this activity in endogenous nitric oxide production and its physiological implications, such as blood pressure regulation and retinal blood supply.

Main Methods:

  • Kinetic analysis of nitrite reductase activity by measuring the reduction of nitrite (NO2-) to nitric oxide (NO) at pH 7.3 and 20.0 °C.
  • Determination of second-order rate constants (kon) for the formation of nitrosylated Nitrobindin (II) (Nb(II)-NO).
  • Investigation of the effect of pH on the reaction rate to elucidate the protonation state involved in the catalytic mechanism.

Main Results:

  • The nitrite reductase activity of Nitrobindin (II) from M. tuberculosis, A. thaliana, D. rerio, and H. sapiens was reported for the first time.
  • Second-order rate constants (kon) for nitrite reduction to NO were determined, ranging from 5.8 to 14 M⁻¹s⁻¹ at pH 7.3 and 20.0 °C.
  • The reaction rate increased with decreasing pH, indicating the involvement of one proton in the conversion of Nb(II) to Nb(II)-NO.

Conclusions:

  • These findings provide the first evidence for nitrite reductase activity in Nitrobindins (II), supporting their role in nitric oxide metabolism.
  • The similar nitrite reductase reactivity between all-β-barrel Nitrobindins and all-α-helical globins suggests conserved functional mechanisms despite distinct protein folds.
  • Distal steric barriers likely play a role in controlling nitrite reductase activity, although more complex regulatory mechanisms may also be involved.