Question

The dehydrogenase enzyme of pentose phashate pathway that catalyze reduction of $\text{NADP}^+$}

• A. Alcohol dehydrogenase
• B. 6-phosphogluconate dehydrogenase
• C. Lactate dehydrogenase
• D. Succinate dehydrogenase

Hint:

The oxidative phase of the Pentose Phosphate Pathway yields exactly $2$ molecules of $\text{NADPH}$ per molecule of Glucose-6-phosphate.
The enzymes responsible are Glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The pentose phosphate pathway (PPP), also known as the phosphogluconate pathway, is an cytosolic metabolic pathway that generates $\text{NADPH}$ for reductive biosynthesis and ribose 5-phosphate for nucleotide synthesis.
The oxidative phase of this pathway contains two key dehydrogenase steps that reduce $\text{NADP}^+$ to $\text{NADPH}$.
Detailed Explanation:
The oxidative branch of the pentose phosphate pathway consists of three reactions:
1. Oxidation of Glucose-6-phosphate to 6-phosphoglucono-$\delta$-lactone, catalyzed by Glucose-6-phosphate dehydrogenase (G6PD), which reduces the first molecule of $\text{NADP}^+$ to $\text{NADPH}$.
2. Hydrolysis of the lactone to 6-phosphogluconate, catalyzed by lactonase.
3. Oxidative decarboxylation of 6-phosphogluconate to Ribulose-5-phosphate, catalyzed by 6-phosphogluconate dehydrogenase.
This third step reduces the second molecule of $\text{NADP}^+$ to $\text{NADPH}$ and releases a molecule of $\text{CO}_2$.
Among the other options:
- Alcohol dehydrogenase catalyzes the interconversion of alcohols and aldehydes using $\text{NAD}^+/\text{NADH}$.
- Lactate dehydrogenase catalyzes the interconversion of pyruvate and lactate using $\text{NAD}^+/\text{NADH}$.
- Succinate dehydrogenase is a citric acid cycle enzyme that uses $\text{FAD}/\text{FADH}_2$.

Step 2: Final Answer:
The enzyme from the pentose phosphate pathway that catalyzes the reduction of $\text{NADP}^+$ is 6-phosphogluconate dehydrogenase.