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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