Q.29 Which one of the following enzymes is located in the outer mitochondrial
membrane?
(A) Citrate synthase
(B) Fumarase
(C) Monoamine oxidase
(D) Succinate dehydrogenase
Monoamine oxidase is the enzyme located in the outer mitochondrial membrane. This multiple-choice question tests knowledge of mitochondrial compartmentalization in cellular respiration and metabolism, key for CSIR NET Life Sciences preparation.
Option Analysis
Citrate synthase catalyzes the first step of the TCA cycle, condensing acetyl-CoA and oxaloacetate to form citrate. It resides in the mitochondrial matrix, synthesized in the cytosol and imported via a targeting signal.
Fumarase converts fumarate to malate in the TCA cycle. Primarily a mitochondrial matrix enzyme, it shows dual localization in some cells (cytosol and matrix), but not the outer membrane.
Monoamine oxidase degrades monoamines like serotonin and dopamine, producing hydrogen peroxide. It is an integral protein of the outer mitochondrial membrane, confirmed across studies in brain, liver, and other tissues.
Succinate dehydrogenase (Complex II) oxidizes succinate to fumarate in the TCA cycle and transfers electrons to ubiquinone. It embeds in the inner mitochondrial membrane, with catalytic subunits facing the matrix.
Correct Answer
(C) Monoamine oxidase. This enzyme’s outer membrane position distinguishes it from TCA cycle enzymes in the matrix or inner membrane.
The outer mitochondrial membrane serves as a selective barrier housing key enzymes like monoamine oxidase, vital for neurotransmitter breakdown and distinct from TCA cycle players such as citrate synthase, fumarase, and succinate dehydrogenase. Understanding outer mitochondrial membrane enzymes clarifies cellular energy dynamics and exam questions on mitochondrial structure.
Mitochondrial Membrane Structure
Mitochondria feature an outer membrane permeable via porins and an inner membrane forming cristae for electron transport. The outer membrane hosts enzymes for lipid metabolism and amine oxidation, while the matrix and inner membrane manage TCA cycle and respiration.
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Outer membrane: Contains monoamine oxidase and fatty acid elongases.
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Intermembrane space: Holds adenylate kinase.
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Inner membrane: Sites for succinate dehydrogenase (Complex II).
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Matrix: Home to citrate synthase and fumarase.
Enzyme Locations and Roles
| Enzyme | Location | Function |
|---|---|---|
| Citrate synthase | Mitochondrial matrix | TCA cycle initiation: acetyl-CoA + oxaloacetate → citrate |
| Fumarase | Primarily matrix (some cytosol) | Fumarate → malate in TCA cycle |
| Monoamine oxidase | Outer mitochondrial membrane | Oxidative deamination of monoamines |
| Succinate dehydrogenase | Inner mitochondrial membrane | Succinate → fumarate; electron transport |
This table highlights why monoamine oxidase uniquely fits outer membrane criteria.
Relevance for CSIR NET
Questions on outer mitochondrial membrane enzymes test TCA cycle compartmentalization. Monoamine oxidase‘s position aids ROS production, linking to neurodegeneration, unlike matrix enzymes focused on ATP yield.
