Related Experiment Video
Updated: Jun 12, 2026
07:59
Estimating Sediment Denitrification Rates Using Cores and N2O Microsensors
Published on: December 6, 2018
Is Nostoc H-NOX a NO sensor or redox switch?
Ah-Lim Tsai1, Vladimir Berka, Faye Martin
1Division of Hematology, Internal Medicine, University of Texas Houston Medical School, Houston, Texas 77030, USA. Ah-lim.tsai@uth.tmc.edu
Biochemistry
|June 25, 2010
Summary
Nostoc sp. H-NOX, a bacterial heme protein, differs functionally from human sGC despite structural similarities. It exhibits unique NO binding and autoxidation, suggesting roles in redox or NO sensing for cyanobacteria.
Area of Science:
- Biochemistry
- Molecular Biology
- Cyanobacteria Research
Background:
- Nostoc sp. H-NOX (Ns H-NOX) is a heme protein in symbiotic cyanobacteria.
- It shares sequence and structural homology with human soluble guanylyl cyclase (sGC), suggesting a NO sensing role.
Purpose of the Study:
- To investigate the functional differences between Ns H-NOX and sGC.
- To elucidate the NO sensing mechanism of Ns H-NOX.
Main Methods:
- UV-vis spectroscopy
- Electron Paramagnetic Resonance (EPR)
- Near-Infrared Magnetic Circular Dichroism (NIR MCD)
- Ligand binding experiments
Main Results:
- Ns H-NOX shows limited pentacoordinate NO heme formation, unlike sGC.
- Two hexacoordinate NO complexes form in Ns H-NOX, dependent on NO concentration.
- Ferric Ns H-NOX autoxidizes and forms a hexacoordinate complex, indicating conformational changes.
Conclusions:
- Ns H-NOX exhibits distinct NO binding and conformational properties compared to sGC.
- These differences suggest Ns H-NOX may function as a redox or NO sensor in cyanobacteria.
Related Concept Videos
02:35Key Elements for Plant Nutrition
Like all living organisms, plants require organic and inorganic nutrients to survive, reproduce, grow and maintain homeostasis. To identify nutrients that are essential for plant functioning, researchers have leveraged a technique called hydroponics. In hydroponic culture systems, plants are grown—without soil—in water-based solutions containing nutrients. At least 17 nutrients have been identified as essential elements required by plants. Plants acquire these elements from the atmosphere, the...
01:30Anoxygenic Photosynthesis
Anoxygenic photosynthesis is a phototrophic process that captures light energy to drive carbon fixation without producing molecular oxygen. Unlike oxygenic photosynthesis, which utilizes water as an electron donor and releases oxygen, anoxygenic phototrophs use alternative electron donors such as hydrogen sulfide (H₂S), elemental sulfur (S⁰), or thiosulfate (S₂O₃²⁻). This process is carried out by diverse groups of bacteria, including purple bacteria, green sulfur bacteria, heliobacteria, and...
01:27Redox Reactions
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...
01:24Redox Reactions
Oxidation-reduction or redox reactions involve the transfer of electrons from one molecule or atom to another. When an atom gains an electron, another atom must lose an electron, meaning oxidation and reduction must occur together. Since the redox occurs in pairs, the atom that gets oxidized is also called the reducing agent or reductant, and the atom that is reduced is also called the oxidizing agent or oxidant. A straightforward way to remember the definitions of oxidation and reduction is...
01:26Redox Titration: Other Oxidizing and Reducing Agents
Besides iodine, other oxidizing or reducing agents can serve as titrants in redox titrations. Common oxidizing titrants include KMnO4, cerium(IV), and K2Cr2O7. The choice of oxidizing titrants depends on factors like stability, cost, analyte strength, and reaction rate between the analyte and titrant. KMnO4 is a strong oxidizing titrant that reduces from Mn(VII) to Mn(II) in a highly acidic solution, simultaneously oxidizing the analyte to a higher oxidation state. In this case, KMnO4 acts as a...
01:23Redox Equilibria: Overview
A reduction-oxidation reaction is commonly called a redox reaction. In a redox reaction, electrons are transferred from one species to another rather than being shared between or among atoms. The reducing agent or reductant is the species that loses electrons and gets oxidized in the process. The species that gains electrons and gets reduced in the process is the oxidizing agent or oxidant. Redox reactions are represented as two separate equations called half-reactions, where one equation...