Major source of NADPH for fatty acid synthesis is:
**Core Concept**
Fatty acid synthesis is a crucial metabolic pathway that generates fatty acids from acetyl-CoA and NADPH. The major source of NADPH for this process is essential for understanding the regulation of lipid metabolism and the role of various enzymes involved.
**Why the Correct Answer is Right**
The correct answer is **Malic Enzyme (ME)**, which generates NADPH during the conversion of malate to pyruvate in the cytosol. This enzyme is a key source of NADPH for fatty acid synthesis, particularly in the liver and adipose tissue. ME uses NADP+ as a cofactor and produces NADPH, which is then used to reduce acetyl-CoA to malonyl-CoA, a critical step in fatty acid synthesis.
**Why Each Wrong Option is Incorrect**
* **Option A:** Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) generates NADH, not NADPH, during glycolysis.
* **Option B:** Isocitrate dehydrogenase (IDH) can generate NADPH in the mitochondria, but it is not the major source of NADPH for fatty acid synthesis.
* **Option D:** Glucose-6-phosphate dehydrogenase (G6PD) generates NADPH during the pentose phosphate pathway, but it is primarily involved in generating NADPH for antioxidant defenses rather than fatty acid synthesis.
**Clinical Pearl / High-Yield Fact**
Remember that malic enzyme (ME) is a key source of NADPH for fatty acid synthesis, particularly in the liver and adipose tissue. This is essential for understanding the regulation of lipid metabolism and the role of various enzymes involved in this process.
**Correct Answer: C. Malic Enzyme (ME)**