This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which of the following enzymes is involved in the process of both cholesterol and ketone bodies metabolism 
Select and explain. 
A. HMG CoA reductase, B. HMG CoA synthase, C. HMG CoA lyase, D. Thiokinase
B: HMG CoA synthase
Answer: B: HMG CoA synthase 
Explanation: HMG CoA synthase 

The first two reactions in the cholesterol synthetic pathway and ketone bodies synthesis are the same


First, two acetyl CoA molecules condense to form acetoacetyl CoA in the presence of thiolase.
Next, the third molecule of acetyl-CoA is added to produce HMG-CoA, a reaction catalyzed by enzyme HMG-CoA synthase.


Liver parenchymal cells contain two isoenzymes of HMG-CoA synthase:-

(1) Cytosolic enzyme → For cholesterol synthesis
Mitochondrial enzyme → For ketone body synthesis