A 44 year old man sustains a myocardial infarction, and is admitted to the hospital from the emergency room. Serum chemistries reveal two-fold elevation of his LDL cholesterol. He is prescribed lovastatin, which acts by inhibiting which of the following enzymes?

**Core Concept**
Lovastatin is a statin, a class of lipid-lowering medications that inhibit a key enzyme in the cholesterol biosynthesis pathway. This enzyme plays a crucial role in the production of cholesterol in the liver.

**Why the Correct Answer is Right**
Lovastatin specifically inhibits HMG-CoA reductase (3-hydroxy-3-methylglutaryl-coenzyme A reductase), which is the rate-limiting enzyme in the cholesterol biosynthesis pathway. By inhibiting HMG-CoA reductase, lovastatin reduces the production of cholesterol in the liver, leading to a decrease in LDL cholesterol levels. This mechanism is crucial in the treatment of hypercholesterolemia and prevention of cardiovascular events.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because lovastatin does not act by inhibiting acetyl-CoA carboxylase, which is involved in fatty acid biosynthesis.

**Option B:** This option is incorrect because lovastatin does not act by inhibiting HMG-CoA synthase, which is involved in the earlier steps of the cholesterol biosynthesis pathway.

**Option C:** This option is incorrect because lovastatin does not act by inhibiting LCAT (lecithin-cholesterol acyltransferase), which is involved in the formation of cholesteryl esters in HDL.

**Option D:** This option is incorrect because lovastatin does not act by inhibiting PCSK9 (proprotein convertase subtilisin/kexin type 9), which is involved in the regulation of LDL receptors.

**Clinical Pearl / High-Yield Fact**
It's essential to note that lovastatin and other statins are contraindicated in patients with active liver disease, as they can cause further liver damage.

**Correct Answer:** C. HMG-CoA reductase

✓ Correct Answer: C. Hydroxymethylglutaryl-CoA reductase