<prompt> Which of the following is the rate-limiting enzyme of bile acid synthesis?microsomal 7-a hydroxylasemitochondrial 7-a hydroxylasemicrosomal 17-a hydroxylasemitochondrial 17-a hydroxylase  <response>: microsomal 7-a hydroxylaseis rate-limiting enzyme of bile acid synthesis The first intermediate in the synthesis of bile acids is 7a-hydroxycholesterol It is catalyzed by the enzyme 7a-hydroxylase, a microsomal CYP450 enzyme, which requires NADPH, oxygen, and vitamin C as co-factors. 