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Related Concept Videos

Inorganic Nitrogen Assimilation01:22

Inorganic Nitrogen Assimilation

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 nitrate reductase...
Rate-Determining Steps03:08

Rate-Determining Steps

Relating Reaction Mechanisms
In a multistep reaction mechanism, one of the elementary steps progresses significantly slower than the others. This slowest step is called the rate-limiting step (or rate-determining step). A reaction cannot proceed faster than its slowest step, and hence, the rate-determining step limits the overall reaction rate.
The concept of rate-determining step can be understood from the analogy of a 4-lane freeway with a short-stretch of traffic-bottleneck caused due to...
Overview of Nitrogen Metabolism01:20

Overview of Nitrogen Metabolism

Nitrogen is a very important element for life because it is a major constituent of proteins and nucleic acids. It is a macronutrient, and in nature, it is recycled from organic compounds and stored in the form of  ammonia, ammonium ions, nitrate, nitrite, or  nitrogen gas by many metabolic processes. Many of these metabolic processes are carried out only by prokaryotes.
The largest pool of nitrogen available in the terrestrial ecosystem is gaseous nitrogen (N2) from the air, but this nitrogen...
The Nitrogen Cycle01:49

The Nitrogen Cycle

Nitrogen atoms, present in all proteins and DNA, are recycled between abiotic and biotic components of the ecosystem. However, the primary form of nitrogen on Earth is nitrogen gas, which cannot be used by most animals and plants. Thus, nitrogen gas must first be converted into a usable form by nitrogen-fixing bacteria before it can be cycled through other living organisms. The use of nitrogen-containing fertilizers and animal waste products in human agriculture has greatly influenced the...
Multi-Step Reactions02:31

Multi-Step Reactions

Chemical reactions often occur in a stepwise fashion involving two or more distinct reactions taking place in a sequence. A balanced equation indicates the reacting species and the product species, but it reveals no details about how the reaction occurs at the molecular level. The reaction mechanism (or reaction path) provides details regarding the precise, step-by-step process by which a reaction occurs. Each of the steps in a reaction mechanism is called an elementary reaction. These...
1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Mechanism01:37

1° Amines to Diazonium or Aryldiazonium Salts: Diazotization with NaNO2 Mechanism

Nitrous acid is a relatively weak and unstable acid prepared in situ by the reaction of sodium nitrite and cold, dilute hydrochloric acid. In an acidic solution, the nitrous acid undergoes protonation when it loses water to form a nitrosonium ion—an electrophile. Nitrous acid reacts with primary amines to give diazonium salts. The reaction is called diazotization of primary amines.

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Related Experiment Video

Updated: May 15, 2026

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O
08:05

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O

Published on: October 7, 2020

Nitrogenase: a draft mechanism.

Brian M Hoffman1, Dmitriy Lukoyanov, Dennis R Dean

  • 1Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.

Accounts of Chemical Research
|January 8, 2013
PubMed
Summary
This summary is machine-generated.

Researchers characterized three nitrogenase intermediates, including the "Janus intermediate" (E(4)), revealing a prompt-alternating (P-A) reaction pathway. This breakthrough explains the enzyme's mechanism and hydrogen production puzzle.

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Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase

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Ammonia Synthesis at Low Pressure
08:14

Ammonia Synthesis at Low Pressure

Published on: August 23, 2017

Related Experiment Videos

Last Updated: May 15, 2026

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O
08:05

Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O

Published on: October 7, 2020

Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase
10:01

Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase

Published on: December 4, 2017

Ammonia Synthesis at Low Pressure
08:14

Ammonia Synthesis at Low Pressure

Published on: August 23, 2017

Area of Science:

  • Biochemistry
  • Bioinorganic Chemistry
  • Enzyme Catalysis

Background:

  • Biological nitrogen fixation is crucial for life, catalyzed by nitrogenase.
  • The detailed catalytic mechanism of nitrogenase has remained elusive.
  • Previous studies lacked characterization of intermediates beyond the resting state (E(0)).

Purpose of the Study:

  • To characterize key intermediate states of nitrogenase during catalysis.
  • To integrate these intermediates into the Lowe-Thorneley (LT) kinetic model.
  • To elucidate the complete catalytic mechanism, including the role of hydrogen production.

Main Methods:

  • Freeze-trapping of catalytic intermediates.
  • Electron nuclear double resonance/hyperfine sublevel correlation (ENDOR/HYSCORE) spectroscopy.
  • Electron spin echo envelope modulation (ESEEM) spectroscopy.

Main Results:

  • Characterization of three freeze-trapped intermediates: E(4) (Janus intermediate), E(7) (H), and E(8) (I).
  • Identification of E(4) as primed for N(2) binding, containing two bridging hydrides.
  • Assignment of I as the final state with ammonia product and H as containing a [-NH(2)] fragment.

Conclusions:

  • Proposed a "prompt-alternating (P-A)" reaction pathway for nitrogenase.
  • Unified the catalytic pathway with the LT kinetic framework.
  • Provided a mechanism explaining obligatory H(2) generation via reductive elimination of hydrides from the E(4) state.