science

Nitrite oxidoreductase

Nitrite oxidoreductase is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Nitrite oxidoreductase rather than just read about it. In short: Nitrite oxidoreductase (NOR or NXR) is an enzyme involved in nitrification. It is the last step in the process of aerobic ammonia oxidation, which is carried out by two groups of nitrifying bacteria: ammonia oxidizers such as Nitrosospira, Nitrosomonas, and Nitrosococcus convert ammonia to nitrite, while nitrite oxidizers such as Nitrobacter and Nitrospira oxidize nitrite to nitrate.

Key takeaways

Nitrite oxidoreductase belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Nitrite oxidoreductase to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Nitrite oxidoreductase from memory before moving on to harder problems.

Reference excerpt

Nitrite oxidoreductase (NOR or NXR) is an enzyme involved in nitrification. It is the last step in the process of aerobic ammonia oxidation, which is carried out by two groups of nitrifying bacteria: ammonia oxidizers such as Nitrosospira, Nitrosomonas, and Nitrosococcus convert ammonia to nitrite, while nitrite oxidizers such as Nitrobacter and Nitrospira oxidize nitrite to nitrate. NXR is responsible for producing almost all nitrate found in nature. NXR belongs to the class of EC numbers 1.7.2- where 1 describes an oxidoreductase, 1.7 describes nitrogen compounds as donors, and 1.7.2- describes cytochromes as acceptors.

Structure NXR is composed of 2 mainly known subunits; nitrite oxidoreductase α (NxrA), and nitrite oxidoreductase β (NxrB) (sometimes written as NorA and NorB). However, recent studies describe a third and fourth subunit, NxrC and NxrT The enzyme's known active site is on the NxrA subunit. There are two types of NXR; one where the NxrA subunit is located in the periplasmic space of a cell, and the other where NxrA is located in the cytoplasm The enzyme is bound to the inner cytoplasmic surface of the bacterial membrane and contains iron-sulfur centers and a molybdenum cofactor. The enzyme is relatively abundant, making up 10-30% of the total protein in these bacteria and forms densely packed structures on the membrane surface. To date, little is known about the exact structure of NXR, but has been discovered to form tubule structures that are hundreds of nanometers long.

Pathway

Reaction

nitrite + acceptor ↽ − − ⇀ nitrate + reduced acceptor {\displaystyle {\ce {{nitrite}+acceptor<=>{nitrate}+reduced\ acceptor}}}

NXR oxidizes nitrite into nitrate in aerobic nitrogen oxidizing bacteria as well as ammonia to nitrite in ammonia oxidizing bacteria or archaea. When it oxidizes nitrite to nitrate, two electrons are shuttled into the respiratory chain. Electrons flow through the subunits of the enzyme through cytochrome c toward the terminal oxidase. This reaction can be reversed to reduce nitrate to nitrite in anaerobic conditions, though the driving force of this reversal is poorly understood.

Metabolism In periplasmic NXR types, protons are derived from water and contribute to proton motive force, which then contributes to the cell's energy budget. However, cytoplasmic NXR does not contribute to proton motive force. The two electrons that are generated from the nitrite oxidation are then donated to molecular oxygen, which yields energy. The NXR pathway for nitrite oxidation generally has a low energy yield (ΔG’ = -74 kJ/mol NO2).

See also Microbial metabolism Ferredoxin—nitrite reductase involved in the assimilation of nitrates by plants

References

External links MetaCyc Pathway: nitrite oxidation

Worked examples

Example 1 — a first encounter with Nitrite oxidoreductase

Start with the simplest possible case. Write down what Nitrite oxidoreductase claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Nitrite oxidoreductase before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Nitrite oxidoreductase ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Nitrite oxidoreductase

In research: Nitrite oxidoreductase appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Nitrite oxidoreductase in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Nitrite oxidoreductase is common in secondary-school and first-year university syllabi. It links to neighbouring topics Enzyme stubs, Oxidoreductases, so understanding it makes those chapters shorter.
In everyday life: Look for Nitrite oxidoreductase outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Nitrite oxidoreductase in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Nitrite oxidoreductase means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Nitrite oxidoreductase out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nitrite oxidoreductase in simple terms?

Why does Nitrite oxidoreductase matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Nitrite oxidoreductase?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Nitrite oxidoreductase.