Excess of leucine causes:
**Core Concept**
Leucine is an essential branched-chain amino acid (BCAA) that plays a crucial role in protein synthesis and metabolism. Its excess can lead to various pathophysiological effects due to its unique metabolic properties.
**Why the Correct Answer is Right**
Excess leucine can cause an increase in the activity of the enzyme branched-chain ketoacid dehydrogenase (BCKAD), leading to the formation of branched-chain ketoacids (BCKAs). BCKAs can inhibit the activity of the pyruvate dehydrogenase complex, leading to decreased pyruvate conversion to acetyl-CoA and subsequently decreased glucose uptake in cells. This can result in hyperglycemia and increased lipid synthesis.
**Why Each Wrong Option is Incorrect**
**Option A:** This is not a known effect of excess leucine. In fact, leucine is known to inhibit protein synthesis when present in excess.
**Option B:** This is not directly related to excess leucine. While leucine can affect insulin sensitivity, it is not the primary cause of insulin resistance.
**Option C:** This is not a known effect of excess leucine. Leucine is actually involved in stimulating protein synthesis, not suppressing it.
**Clinical Pearl / High-Yield Fact**
It's essential to note that excess leucine can also lead to the development of ketoacidosis, particularly in patients with type 1 diabetes. This is because the BCKA byproducts can accumulate and lead to a metabolic state similar to diabetic ketoacidosis.
**Correct Answer:** D. Increased lipid synthesis and hyperglycemia.