Question:
Which of the following enzyme is involved in the protection of cells from reactive oxygen species?
Which of the following enzyme is involved in the protection of cells from reactive oxygen species?
Show Hint
Look for the enzyme that is not part of glycolysis; it belongs to the pentose phosphate pathway and supplies NADPH for the glutathione antioxidant system.
Updated On: Aug 7, 2026
- Hexokinase
- Glucose 6-phosphate dehydrogenase
- Enolase
- Pyruvate kinase
Show Solution
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Question:
We need to pick, among four sugar metabolism enzymes, the one whose activity actually protects the cell from reactive oxygen species (ROS) such as hydrogen peroxide and superoxide.
Step 2: Key Formula or Approach:
Glucose 6-phosphate dehydrogenase (G6PD) is the first and rate limiting enzyme of the pentose phosphate pathway (PPP), not glycolysis. It catalyzes:
\[ \text{Glucose 6-phosphate} + NADP^+ \rightarrow \text{6-phosphogluconolactone} + NADPH + H^+ \]
The NADPH made here is the cell's main supply of reducing power for antioxidant defense.
Step 3: Detailed Explanation:
NADPH keeps the enzyme glutathione reductase running, which regenerates reduced glutathione (GSH) from its oxidized form (GSSG).
Reduced glutathione is then used by glutathione peroxidase to detoxify hydrogen peroxide and lipid peroxides, turning ROS into water.
So the chain is: G6PD makes NADPH, NADPH regenerates GSH, GSH clears ROS. Cells, red blood cells especially, with low G6PD activity cannot keep up this supply and suffer oxidative damage, which is why G6PD deficiency in humans causes hemolytic anemia after oxidative stress, for example after eating fava beans or taking certain drugs.
Hexokinase (option A) only phosphorylates glucose to glucose 6-phosphate, the entry step of glycolysis; it has no antioxidant role.
Enolase (option C) converts 2-phosphoglycerate to phosphoenolpyruvate in glycolysis, again a purely energy yielding step with no link to ROS defense.
Pyruvate kinase (option D) converts phosphoenolpyruvate to pyruvate, the last glycolytic step, and also has no antioxidant function; in fact, pyruvate kinase deficiency causes a different kind of hemolytic anemia, due to energy failure, not oxidative stress.
Step 4: Final Answer:
Glucose 6-phosphate dehydrogenase protects cells from reactive oxygen species by generating the NADPH needed to keep glutathione in its reduced, ROS-scavenging form. \[ \boxed{\text{(B) Glucose 6-phosphate dehydrogenase}} \]
We need to pick, among four sugar metabolism enzymes, the one whose activity actually protects the cell from reactive oxygen species (ROS) such as hydrogen peroxide and superoxide.
Step 2: Key Formula or Approach:
Glucose 6-phosphate dehydrogenase (G6PD) is the first and rate limiting enzyme of the pentose phosphate pathway (PPP), not glycolysis. It catalyzes:
\[ \text{Glucose 6-phosphate} + NADP^+ \rightarrow \text{6-phosphogluconolactone} + NADPH + H^+ \]
The NADPH made here is the cell's main supply of reducing power for antioxidant defense.
Step 3: Detailed Explanation:
NADPH keeps the enzyme glutathione reductase running, which regenerates reduced glutathione (GSH) from its oxidized form (GSSG).
Reduced glutathione is then used by glutathione peroxidase to detoxify hydrogen peroxide and lipid peroxides, turning ROS into water.
So the chain is: G6PD makes NADPH, NADPH regenerates GSH, GSH clears ROS. Cells, red blood cells especially, with low G6PD activity cannot keep up this supply and suffer oxidative damage, which is why G6PD deficiency in humans causes hemolytic anemia after oxidative stress, for example after eating fava beans or taking certain drugs.
Hexokinase (option A) only phosphorylates glucose to glucose 6-phosphate, the entry step of glycolysis; it has no antioxidant role.
Enolase (option C) converts 2-phosphoglycerate to phosphoenolpyruvate in glycolysis, again a purely energy yielding step with no link to ROS defense.
Pyruvate kinase (option D) converts phosphoenolpyruvate to pyruvate, the last glycolytic step, and also has no antioxidant function; in fact, pyruvate kinase deficiency causes a different kind of hemolytic anemia, due to energy failure, not oxidative stress.
Step 4: Final Answer:
Glucose 6-phosphate dehydrogenase protects cells from reactive oxygen species by generating the NADPH needed to keep glutathione in its reduced, ROS-scavenging form. \[ \boxed{\text{(B) Glucose 6-phosphate dehydrogenase}} \]
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