This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Physiology
The rate-limiting step in the synthesis of coisol is catalyzed by 
Select and explain. 
A. 21-Hydroxylase, B. 3b-Hydroxysteroid dehydrogenase, C. Cholesterol side-chain cleavage enzyme, D. 11b-Hydroxylase
C: Cholesterol side-chain cleavage enzyme
Answer: C: Cholesterol side-chain cleavage enzyme 
Explanation: The first and rate-limiting step in all steroid biosynthesis is catalyzed by cholesterol sidechain cleavage enzyme, resulting in pregnenolone and isocaproic acid.