biology

Malate oxidase

Malate oxidase 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 Malate oxidase rather than just read about it. In short: In enzymology, a malate oxidase (EC 1.1.3.3) is an enzyme that catalyzes the chemical reaction (S)-malate + O2 ⇌ {\displaystyle \rightleftharpoons } oxaloacetate + H2O2 Thus, the two substrates of this enzyme are (S)-malate and O2, whereas its two products are oxaloacetate and H2O2. This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with oxygen as acceptor.

Key takeaways

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

Reference excerpt

In enzymology, a malate oxidase (EC 1.1.3.3) is an enzyme that catalyzes the chemical reaction

(S)-malate + O2 ⇌ {\displaystyle \rightleftharpoons } oxaloacetate + H2O2 Thus, the two substrates of this enzyme are (S)-malate and O2, whereas its two products are oxaloacetate and H2O2. This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with oxygen as acceptor. The systematic name of this enzyme class is (S)-malate:oxygen oxidoreductase. Other names in common use include FAD-dependent malate oxidase, malic oxidase, and malic dehydrogenase II. This enzyme participates in pyruvate metabolism. It employs one cofactor, FAD. The enzyme is commonly localized on the inner surface of the cytoplasmic membrane although another family member (malate dehydrogenase 2 (NAD)) is found in the mitochondrial matrix.

Mechanisms Malate oxidase belongs to the family of malate dehydrogenases (EC 1.1.1.37) (MDH) that reversibly catalyze the oxidation of malate to oxaloacetate by means of the reduction of a cofactor. The most common isozymes of malate dehydrogenase use NAD+ or NADP+ as a cofactor to accept electrons and protons.

However, the main difference of malate oxidase is that it normally employs FAD as redox partner as alternative. Contrary to pyridine based NAD+/NADP+, FAD comprises a quinone moiety, which is reduced by the forward reaction. FAD is thereby converted to FADH2. In this case, malate oxidase is qualified as malate dehydrogenase (quinone). In mutant strains of Escherichia coli lacking the activity of NAD-dependent malate dehydrogenase, malate oxidase is expressed. It is suggested that products of malate dehydrogenase could be responsible for repression of malate oxidase. This would confirm the existence of a family of structurally different malate dehydrogenases. Malate oxidase is induced only in cells, which completely lack the activity of NAD-specific malate dehydrogenase. Irradiation of cytoplasm membranes of Mycobacterium smegmatis with ultraviolet light (360 nm) for 10 minutes resulted in about a 50% loss of malate oxidase activity. The addition of vitamin K, containing a functional naphthoquinone ring, restores the oxidation activity of malate oxidase. The quinone functionality of vitamin K can hence act as an alternative for FAD.

Biological Reference However, instead of using NAD+, NADP+ or FAD as cofactors, malate oxidase can also shift to oxygen as oxidant and proton acceptor.

(S)-malate + O2 ⇌ oxaloacetate + H2O2 Although seemingly unlikely because of its reactive oxidative character, hydrogen peroxide is found in biological systems including the human body. It signals oxidative stress from wounds to the immune system to recruit white blood cells for the healing process. A study in Nature suggested that asthma sufferers have higher levels of hydrogen peroxide in their lungs than healthy people, which would explain why these patients also have inappropriate levels of white blood cells in their lungs. Asthma sufferers might have certain variations in cellular levels of NAD+/NADP+ or FAD, which causes malate oxidase to shift to oxygen as its oxidant, due to its high abundancy in the lungs. This could be a possible explanation for the elevated levels of hydrogen peroxide in their lungs.

Uses Topical compositions of malate oxidase combined with suitable disease-detecting biomarkers and a chemiluminescent dye are used in disease detecting systems. The biomarker activates the malate oxidase to generate hydrogen peroxide that excites the light-emitting dye, which exhibits chemiluminescence in the presence of the peroxide. Such contemporary compositions are thus used as a diagnostic tool for detecting diseases. In a similar method, malate oxidase is used in the transcutaneous measurement of the amount of a substrate in blood. The method is conducted by contacting the skin with the enzyme, reacting the substrate with the enzyme and directly detecting the amount of H2O2 produced as a measure of the amount of substrate in the blood, with use of a hydrogen peroxide electrode. Further dermatological applications are in drugs or cosmetic agents, comprising a suitable substrate and malate oxidase as hydrogen peroxide producing enzyme for skin lightening and age spots or freckles. Other illustrative uses that employ the capacity of malate oxidase to yield hydrogen peroxide in the presence of a suitable substrate, including malate, are found in toothpaste to remove bacterial plaque, cleaning compositions for removing blood stains and the like, and in the removal of chewing gum lumps stuck on surfaces by enzymatic degradation. Malate oxidase is also employed in the inhibition of corrosion by dissolved oxygen in water by converting it to hydrogen peroxide, which is subsequently broken down into water and oxygen by catalase.

References

COHN DV (1958). "The enzymatic formation of oxalacetic acid by nonpyridine nucleotide malic dehydrogenase of Micrococcus lysodeikticus". J. Biol. Chem. 233 (2): 299–304. doi:10.1016/S0021-9258(18)64754-4. PMID 13563491. Narindrasorasak S, Goldie AH, Sanwal BD (1979). "Characteristics and regulation of a phospholipid-activated malate oxidase from Escherichia coli". J. Biol. Chem. 254 (5): 1540–5. doi:10.1016/S0021-9258(17)37805-5. PMID 368072.

Illustrations

Malate oxidase: Reversible reaction of (S)-malate to oxaloactetate with oxygen as the proton acceptor (oxidant), catalyzed by malate oxidase. — Reversible reaction of (S)-malate to oxaloactetate with oxygen as the proton acceptor (oxidant), catalyzed by malate oxidase.

Worked examples

Example 1 — a first encounter with Malate oxidase

Start with the simplest possible case. Write down what Malate oxidase 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 Malate oxidase 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 Malate oxidase 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 Malate oxidase

In research: Malate oxidase 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 Malate oxidase 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: Malate oxidase is common in secondary-school and first-year university syllabi. It links to neighbouring topics EC 1.1.3, Enzymes of unknown structure, Flavoproteins, so understanding it makes those chapters shorter.
In everyday life: Look for Malate oxidase 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 Malate oxidase in 20 minutes

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

Frequently asked questions

What is Malate oxidase in simple terms?

In enzymology, a malate oxidase (EC 1.1.3.3) is an enzyme that catalyzes the chemical reaction (S)-malate + O2 ⇌ {\displaystyle \rightleftharpoons } oxaloacetate + H2O2 Thus, the two substrates of this enzyme are (S)-malate and O2, whereas its two products are oxaloacetate and H2O2. This enzyme bel…

Why does Malate oxidase 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 Malate oxidase?

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 Malate oxidase.