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Table 1 Major classical and alternative pathway enzymes with subcellular location, reaction type and position of structure modification, and product(s) formed

From: The influence of biological sex and sex hormones on bile acid synthesis and cholesterol homeostasis

Major enzymesLocalizationReactionPosition on CholesterolProduct
Classical pathway
CYP7A1Endoplasmic ReticulumSterol ring modificationC77a-hydroxycholesterol
AKR1D1CytosolSterol ring modificationC55b-reduced intermediates
CYP8B1Endoplasmic ReticulumSterol ring modificationC127a, 12a-dihydroxy-4-cholestan-3-one
CYP27A1MitochondriaSide chain modificationC2727-hydroxycholesterol
CYP3A4Endoplasmic ReticulumSterol ring modificationC44alpha-hydroxy-cholesterol
Alternative pathway
CYP27A1MitochondriaSide chain modificationC2727a-hydroxylcholesterol 25a-hydroxycholesterol 24a-hydroxycholesterol
CYP7B1Endoplasmic ReticulumSterol ring modificationC77a-hydroxylated intermediates
AKR1D1Cytosol  5b-reduced intermediates
CYP27A1MitochondriaSide chain modificationC27CDCA