Q.5 Oxidases act as
l. Use oxygen as an electron acceptor but donot incorporate it into the substrate.
2. Directly incorporate oxygen into the substrate
3. Use H2O2 as an electron acceptor
4. Use molecules other than oxygen (eg : NAD¯) as an electron acceptor
Correct Answer: Option 1
Oxidases are enzymes that utilize molecular oxygen (O₂) as the terminal electron acceptor in oxidation reactions, reducing it to water or hydrogen peroxide without incorporating oxygen atoms into the substrate itself.
Option Analysis
Option 1: Correct
Oxidases transfer electrons to O₂, typically producing H₂O₂ or H₂O, but do not insert oxygen into the substrate; this distinguishes them from oxygenases.
Examples include cytochrome c oxidase, which reduces O₂ to H₂O in the electron transport chain.
Option 2: Incorrect
Direct incorporation of oxygen into the substrate defines oxygenases (mono- or dioxygenases), not oxidases; e.g., cytochrome P450 inserts one O atom as a hydroxyl group.
Option 3: Incorrect
Oxidases may produce H₂O₂ as a byproduct (e.g., flavin-dependent oxidases), but they do not use it as the electron acceptor; O₂ is the acceptor.
Option 4: Incorrect
This describes dehydrogenases (e.g., using NAD⁺/NADP⁺), not oxidases, which specifically require O₂ as the electron acceptor.
Introduction to Oxidases
Oxidases act as key enzymes in aerobic respiration and metabolism, where the correct statement is that they use oxygen as an electron acceptor without incorporating it into the substrate, vital for competitive exams like GATE Life Sciences. This differentiates them from oxygenases and supports electron transport chain functions in mitochondria.
Defining Oxidases
Oxidases catalyze two-electron transfers from substrates to O₂, yielding H₂O₂ or H₂O via cofactors like flavins or metals.
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No oxygen insertion occurs; O₂ serves solely as oxidant.
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Role: Detoxification, energy production (e.g., cytochrome c oxidase in Complex IV).
Oxidases vs. Oxygenases
| Feature | Oxidases | Oxygenases |
|---|---|---|
| O₂ Role | Electron acceptor (to H₂O/H₂O₂) | Incorporated into substrate |
| Products | Oxidized substrate + H₂O/H₂O₂ | Hydroxylated/oxygenated substrate |
| Examples | Cytochrome c oxidase, amine oxidase | Cytochrome P450, lipoxygenase |
| Mechanism | Electron transfer only | O atom insertion (mono-/dioxygenase) |
This comparison highlights why option 1 is the correct statement for “oxidases act as.”
Exam Tips for Life Sciences
For queries like “Oxidases act as,” focus on O₂ as acceptor without incorporation to score in GATE/Biotech exams. Common error: Confusing with oxygenases (option 2); recall oxidases reduce O₂ externally.
