Question:
Which of the following enzymes contain an unusual amino acid viz. selenocysteine, at its active site?
Which of the following enzymes contain an unusual amino acid viz. selenocysteine, at its active site?
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Glutathione peroxidase and iodothyronine deiodinase are classic examples of selenoproteins in biochemistry that contain selenocysteine at their catalytic centers.
Updated On: Jul 31, 2026
- Ascorbate peroxidase
- Glutathione peroxidase
- Superoxide dismutase
- Catalase
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Selenocysteine is considered the 21st proteinogenic amino acid.
It contains a selenium atom in place of the sulfur atom found in standard cysteine, which alters its chemical reactivity.
Step 2: Detailed Explanation:
Glutathione peroxidase (GPx) is an important antioxidant enzyme that protects cells from oxidative damage by reducing hydrogen peroxide and organic hydroperoxides to water and alcohols, using glutathione as a reducing agent.
The catalytic mechanism of glutathione peroxidase depends on a selenocysteine residue located within its active site.
The selenium atom undergoes a reversible oxidation-reduction cycle during catalysis, reacting much faster with peroxides than standard sulfur-containing cysteine residues would.
This unique selenium group is essential for the high catalytic efficiency of the enzyme.
Step 3: Final Answer:
Therefore, Glutathione peroxidase contains selenocysteine in its active site, which corresponds to option (B).
Selenocysteine is considered the 21st proteinogenic amino acid.
It contains a selenium atom in place of the sulfur atom found in standard cysteine, which alters its chemical reactivity.
Step 2: Detailed Explanation:
Glutathione peroxidase (GPx) is an important antioxidant enzyme that protects cells from oxidative damage by reducing hydrogen peroxide and organic hydroperoxides to water and alcohols, using glutathione as a reducing agent.
The catalytic mechanism of glutathione peroxidase depends on a selenocysteine residue located within its active site.
The selenium atom undergoes a reversible oxidation-reduction cycle during catalysis, reacting much faster with peroxides than standard sulfur-containing cysteine residues would.
This unique selenium group is essential for the high catalytic efficiency of the enzyme.
Step 3: Final Answer:
Therefore, Glutathione peroxidase contains selenocysteine in its active site, which corresponds to option (B).
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