<prompt> 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?Acetyl-CoA carboxylaseCarbamoyl phosphate synthetase IHydroxymethylglutaryl-CoA reductasePyruvate dehydrogenase  <response>: Hydroxymethylglutaryl-CoA reductase HMG-CoA reductase catalyzes the rate-limiting step in cholesterol synthesis, in which HMG-CoA formed from 3 acetyl-CoA molecules is reduced to mevalonic acid, using 2 NADPH. Lovastatin and pravastatin reduce cholesterol synthesis and lower serum cholesterol levels by inhibiting this enzyme. Lovastatin is metabolized by the CYP3A isoform of cytochrome P450. In contrast, gemfibrozil and clofibrate lower cholesterol by increasing the activity of lipoprotein lipase, which is produced by the endothelial cells of the vasculature of adipose and muscle tissue. Acetyl-CoA carboxylase catalyzes the first step in fatty acid synthesis. Carbamoyl phosphate synthetase catalyzes the rate-limiting step in urea synthesis. Pyruvate dehydrogenase catalyzes the transition step between glycolysis and the TCA Krebs cycle. Ref: Botham K.M., Mayes P.A. 2011. Chapter 26. Cholesterol Synthesis, Transpo, Excretion. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell Eds, Harpers Illustrated Biochemistry, 29e. 