Which of the following enzymes would be expected to exert the greatest negative effect on the rate of cholesterol biosynthesis?
A) acetyl-CoA carboxylase (ACC)
B) AMP-regulated kinase (AMPK)
C) cGMP-dependent protein kinase (PKG)
D) HMG-CoA reductase (HMGR)
E) malonyl-CoA decarboxylase (MCD)

Question

Quizplus · Accepted Answer

AMP-regulated kinase (AMPK) negatively regulates cholesterol biosynthesis by phosphorylating and inhibiting HMG-CoA reductase, the rate-limiting enzyme in the cholesterol biosynthesis pathway.  HMG-CoA reductase is the rate-limiting enzyme of cholesterol biosynthesis and the major site for regulation of this metabolic pathway. Regulation of HMGR through covalent modification occurs as a result of phosphorylation and dephosphorylation. The enzyme is most active in its unmodified form. Phosphorylation of the enzyme decreases its activity. HMGR is phosphorylated by AMPK, which itself is activated via phosphorylation. Increased AMPK activity would, therefore, have a significant negative impact on the rate of HMGR activity.

Which of the Following Enzymes Would Be Expected to Exert