biology

Trimethylamine N-oxide reductase

Trimethylamine N-oxide reductase is a biology 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 Trimethylamine N-oxide reductase rather than just read about it. In short: Trimethylamine N-oxide reductase (TOR or TMAO reductase, EC 1.7.2.3) is a microbial enzyme that can reduce trimethylamine N-oxide (TMAO) into trimethylamine (TMA), as part of the electron transport chain. The enzyme has been purified from E. coli and the photosynthetic bacteria Roseobacter denitrificans.

Key takeaways

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

Reference excerpt

Trimethylamine N-oxide reductase (TOR or TMAO reductase, EC 1.7.2.3) is a microbial enzyme that can reduce trimethylamine N-oxide (TMAO) into trimethylamine (TMA), as part of the electron transport chain. The enzyme has been purified from E. coli and the photosynthetic bacteria Roseobacter denitrificans. Trimethylamine oxide is found at high concentrations in the tissues of fish, and the bacterial reduction of this compound to foul-smelling trimethylamine is a major process in the spoilage of fish.

Classification TMAO reductase has an enzyme commission (EC) number of 1.7.2.3. EC numbers are a system of enzyme nomenclature, and each part of this nomenclature refers to a progressive classification of the enzyme with regards to its reaction. The first number defines the reaction type, the second number provides information on involved compounds, the third number specifies the type of reaction, and the fourth number completes the unique serial number for each enzyme. Trimethylamine N-oxide reductase has the EC number 1.7.2.3, and these components refer to the following enzyme classifications:

EC 1 enzymes are oxidoreductase enzymes, where an oxidation reduction reaction occurs, and the substrate being oxidized is either an oxygen or hydrogen donor EC 1.7 enzymes act on other nitrogenous compounds as donors EC 1.7.2 enzymes have a cytochrome as an acceptor EC 1.7.2.3 is the enzyme TMAO reductase, which reduces the cytochrome TorC

Species distribution TMAO is an organic osmolyte that has the useful biological function of protecting proteins against denaturing stresses such as high concentration of urea. Various bacteria grow anaerobically using TMAO as an alternative electron transport chain, allowing for growth on non-fermentable carbon sources such as glycerol. Bacteria capable of reducing TMAO to TMA are found throughout three different ecological niches. TMAO-reducing, to date, has been observed in marine bacteria, photosynthetic bacteria living in shallow ponds, and in enterobacteria. TMAO reductases have been studied in several organisms, and a common conserved feature is the presence of a molybdenum cofactor in all the known terminal enzymes. Based on their substrate specificity, these enzymes can be divided into two groups:

TMAO reductases which have high substrate specificity DMSO/TMAO reductases which can reduce a broad range of N and S-oxide substrates. The first group consists of species such as Escherichia coli, Shewanella putrefaciens, and Roseobacter denitrificans while the second group consists of species such as Proteus vulgaris, Rhodobacter capsulatus, and Rhodobacter sphaeroides. The TMAO respiratory system has been mostly widely studied at the molecular level in E. coli and Rhodobacter species.

Reaction mechanism In E. coli, TMAO reductase is encoded by the torCAD operon. The torC gene encodes a pentahemic c-type cytochrome (TorC). TorC is likely to transfer electrons directly to the periplasmic TorA terminal enzyme encoded by the torA gene. The anaerobic expression of the torCAD operon is strictly controlled by the presence of TMAO or related compounds. There are several different metabolic pathways that involve TMAO and TMA. The reduction of TMAO to TMA, catalyzed by TMAO reductase, as part of the electron transport chain follows the following reaction: NADH + H+ + trimethylamine N-oxide ⇌ {\displaystyle \rightleftharpoons } NAD+ + trimethylamine + H2O However, both the R. denitrificans and E. coli enzymes can accept electrons from cytochromes:

trimethylamine + 2 (ferricytochrome c)-subunit + H2O → trimethylamine N-oxide + 2 (ferrocytochrome c)-subunit + 2 H+ Other reactions involving TMAO and TMA include:

The oxidation of TMA to TMAO, which occurs in some methylotrophs as an initial step in utilizing TMA as a source of carbon The demethylation of TMAO to dimethylamine and formaldehyde by methylotrophs The oxidative demethylation of TMA to dimethylamine and formaldehyde by methylotrophs The production of methane from TMA and other methylamines by some methanogens

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Trimethylamine N-oxide reductase

Start with the simplest possible case. Write down what Trimethylamine N-oxide reductase claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, 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 Trimethylamine N-oxide reductase 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 Trimethylamine N-oxide reductase 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 Trimethylamine N-oxide reductase

In research: Trimethylamine N-oxide reductase appears in biology 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 Trimethylamine N-oxide reductase 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: Trimethylamine N-oxide reductase is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cellular respiration, EC 1.7.2, Metabolism, so understanding it makes those chapters shorter.
In everyday life: Look for Trimethylamine N-oxide reductase 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 Trimethylamine N-oxide reductase in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Trimethylamine N-oxide reductase 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 Trimethylamine N-oxide reductase out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Trimethylamine N-oxide reductase in simple terms?

Why does Trimethylamine N-oxide reductase matter?

Because it connects several biology 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 Trimethylamine N-oxide reductase?

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 Trimethylamine N-oxide reductase.