Rate limiting enzyme in bile acid synthesis?

Rate limiting enzyme in bile acid
synthesis ?
a) Desmolase
b) 21 α-hydroxylase
c) 7α-hydroxylase
d) 12α-hydroxylase

Correct Answer - C
Ans. is ‘c’ i.e., 7α-hydroxylase
About half of the cholesterol in the body is ultimately metabolized to
bile acids.
The primary bile acids are synthesized from cholesterol in liver.
These are cholic acid and chenodeoxycholic acid.
Rate limiting enzyme in primary bile acids synthesis is 7α -
hydroxylase (cholesterol 7α - hydroxylase).
This enzyme is inhibited by bile acids and induced by cholesterol.
Thyroid hormones induce transcription of 7a-hydroxylase, thus in
patients with hypothyroidism plasma cholesterol tends to rise
(because of inhibition of 7α-hydroxylase which in turn inhibits
conversion of cholesterol to bile acids).