biology

NADH peroxidase

NADH peroxidase 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 NADH peroxidase rather than just read about it. In short: In enzymology, a NADH peroxidase (EC 1.11.1.1) is an enzyme that catalyzes the chemical reaction NADH + H+ + H2O2 ⇌ {\displaystyle \rightleftharpoons } NAD+ + 2 H2O The presumed function of NADH peroxidase is to inactivate H2O2 generated within the cell, for example by glycerol-3-phosphate oxidase during glycerol metabolism or dismutation of superoxide, before the H2O2 causes damage to essential cellular components…

Key takeaways

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

Reference excerpt

In enzymology, a NADH peroxidase (EC 1.11.1.1) is an enzyme that catalyzes the chemical reaction

NADH + H+ + H2O2 ⇌ {\displaystyle \rightleftharpoons } NAD+ + 2 H2O The presumed function of NADH peroxidase is to inactivate H2O2 generated within the cell, for example by glycerol-3-phosphate oxidase during glycerol metabolism or dismutation of superoxide, before the H2O2 causes damage to essential cellular components. The 3 substrates of this enzyme are NADH, H+, and H2O2, whereas its two products are NAD+ and H2O. It employs one cofactor, FAD, however no discrete FADH2 intermediate has been observed. This enzyme belongs to the family of oxidoreductases, specifically those acting on a peroxide as acceptor (peroxidases). The systematic name of this enzyme class is NADH:hydrogen-peroxide oxidoreductase. Other names in common use include DPNH peroxidase, NAD peroxidase, diphosphopyridine nucleotide peroxidase, NADH-peroxidase, nicotinamide adenine dinucleotide peroxidase, and NADH2 peroxidase.

Structure The crystal structure of NADH peroxidase resembles glutathione reductase with respect to chain fold and location as well as conformation of the prosthetic group FAD His10 of the NADH peroxidase is located near the N-terminus of the R1 helix within the FAD-binding site. One of the oxygen atoms of Cys42-SO3H is hydrogen-bonded both to the His10 imidazole and to Cys42 N terminus. The His10 functions in part to stabilize the unusual Cys42-SOH redox center. Arg303 also stabilizes the Cys42-SO3H. Glu-14 participates in forming the tight dimer interface that limits solvent accessibility, important for maintaining the oxidation state of the sulfenic acid.

Reaction mechanism The NADH peroxidase from Enterococcus faecalis is unique in that it utilizes the Cys42 thiol/sulfenic acid (-SH/-SOH) redox couple in the heterolytic cleavage of the peroxide bond to catalyze the two-electron reduction of hydrogen peroxide to water. The kinetic mechanism of the wild-type peroxidase involves (1) NADH reduction of E(FAD, Cys42-SOH) to EH2(FAD, Cys42-SH) in an initial priming step; (2) rapid binding of NADH to EH2; (3) reduction of H2O2 by the Cys42-thiolate, yielding E•NADH; and (4) rate-limiting hydride transfer from bound NADH, regenerating EH2. No discrete FADH2 intermediate has been observed, however, and the precise details of Cys42-SOH reduction have not been elucidated.

E + NADH → (EH2'•NAD+)* → EH2'•NAD+ → EH2 + NAD+ + H2O EH2 + NADH → EH2•NADH* EH2•NADH* + H2O2 → E•NADH + H2O E•NADH + H+ → EH2•NAD+ + H2O EH2•NAD+ → EH2 + NAD+ Inhibitors include Ag+, Cl−, Co2+, Cu2+, Hg2+, NaN3, Pb2+, and SO42−. At suboptimal H2O2 concentrations and concentrations of NADH that are saturating, NADH inhibits the peroxidase activity of the NADH peroxidase by converting the enzyme to an unstable intermediate. NAD+ behaves as an activator by reversing the equilibria that lead to the unstable intermediate, thus converting the enzyme to the kinetically active complex that reduces H2O2.

Biological Function NADH eliminates potentially toxic hydrogen peroxide under aerobic growth conditions and represents an enzymatic defense available against H2O2-mediated oxidative stress. Second, the enzyme presents an additional mechanism for regeneration of the NAD+ essential to the strictly fermentative metabolism of this organism. The enzyme may also protect against exogenous H2O2 and contribute to bacterial virulence. The actual function of NADH peroxidases and oxidases in plants is still unclear, but they could act in early signaling of oxidative stress through producing H2O2. An alternative role may include regulation of H2O2 formation by NADH peroxidase and oxidase in cell wall loosening and reconstruction.

References

Illustrations

Worked examples

Example 1 — a first encounter with NADH peroxidase

Start with the simplest possible case. Write down what NADH peroxidase 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 NADH peroxidase 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 NADH peroxidase 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 NADH peroxidase

In research: NADH peroxidase 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 NADH peroxidase 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: NADH peroxidase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 1.11.1, Enzymes of known structure, Flavoproteins, so understanding it makes those chapters shorter.
In everyday life: Look for NADH peroxidase 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 NADH peroxidase in 20 minutes

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

Frequently asked questions

What is NADH peroxidase in simple terms?

In enzymology, a NADH peroxidase (EC 1.11.1.1) is an enzyme that catalyzes the chemical reaction NADH + H+ + H2O2 ⇌ {\displaystyle \rightleftharpoons } NAD+ + 2 H2O The presumed function of NADH peroxidase is to inactivate H2O2 generated within the cell, for example by glycerol-3-phosphate oxidase…

Why does NADH peroxidase 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 NADH peroxidase?

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 NADH peroxidase.