Cholesterol-5,6-oxide hydrolase (, ''cholesterol-epoxide hydrolase'', ''ChEH'') is an
enzyme
An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...
with
systematic name
A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature.
A semisystematic name or semitrivi ...
''5,6alpha-epoxy-5alpha-cholestan-3beta-ol hydrolase''. This enzyme
catalyses the following
chemical reaction
A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...
: (1) 5,6alpha-epoxy-5alpha-cholestan-3beta-ol + H
2O
5alpha-cholestane-3beta,5alpha,6beta-triol
: (2) 5,6beta-epoxy-5beta-cholestan-3beta-ol + H
2O
5alpha-cholestane-3beta,5alpha,6beta-triol
The enzyme works equally well with either
epoxide
In organic chemistry, an epoxide is a cyclic ether, where the ether forms a three-atom ring: two atoms of carbon and one atom of oxygen. This triangular structure has substantial ring strain, making epoxides highly reactive, more so than other ...
as substrate on rat liver microsomes. The ChEH is an intracellular en membranous enzyme localized mainly on the endoplasmic reticulum of cells. Its molecular characterization revealed it is composed of two proteinaceous sub-units: the 3beta-hydroxysteroid delta8-delta7-isomerase (D8D7I), also known as the
emopamil binding protein (EBP), which is the catalytic subunit, and the 3beta-hydroxysteroid delta7 reductase (DHCR7), which is the regulatory subunit. The ChEH is the "so called" microsomal antiestrogen binding site (AEBS), a secondary target of the antitumor drug tamoxifen and related compounds. The ChEH is inhibited by different pharmacological classes of drugs including anticancer drugs such as tamoxifen and natural substances such as ring B-oxysterols and poly-unsaturated fatty acids.
References
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