The first step in synthesis of steroids is derived from the cleavage of cholesterol. What is the enzyme responsible for the cleavage of 20,22-dehydrocholesterol to pregnenolone?

The enzyme responsible for the cleavage of 20,22-dehydrocholesterol to pregnenolone is termed Delta 5-3 beta-hydroxysteroid dehydrogenase ( 3B HSD). Pregnenolone is a precursor to progesterone. Conversion to progesterone is necessary for eventual synthesis of testosterone and estrogen. Although there are different enzymes for their production, progesterone conveed from cholesterol is of primary impoance. Ref: Weil P. (2011). Chapter 41. The Diversity of the Endocrine System. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.