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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 enzymes Localization Reaction Position on Cholesterol Product
Classical pathway
CYP7A1 Endoplasmic Reticulum Sterol ring modification C7 7a-hydroxycholesterol
AKR1D1 Cytosol Sterol ring modification C5 5b-reduced intermediates
CYP8B1 Endoplasmic Reticulum Sterol ring modification C12 7a, 12a-dihydroxy-4-cholestan-3-one
CYP27A1 Mitochondria Side chain modification C27 27-hydroxycholesterol
CYP3A4 Endoplasmic Reticulum Sterol ring modification C4 4alpha-hydroxy-cholesterol
Alternative pathway
CYP27A1 Mitochondria Side chain modification C27 27a-hydroxylcholesterol 25a-hydroxycholesterol 24a-hydroxycholesterol
CYP7B1 Endoplasmic Reticulum Sterol ring modification C7 7a-hydroxylated intermediates
AKR1D1 Cytosol    5b-reduced intermediates
CYP27A1 Mitochondria Side chain modification C27 CDCA