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Text
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<a href="http://doi.org/10.1111/j.1432-1033.1993.tb18082.x" target="_blank" rel="noreferrer noopener">http://doi.org/10.1111/j.1432-1033.1993.tb18082.x</a>
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Pages
705-710
Issue
3
Volume
215
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Title
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CHOLESTEROL 7-ALPHA-HYDROXYLASE IS UP-REGULATED BY THE COMPETITIVE INHIBITOR 7-OXOCHOLESTEROL IN RAT-LIVER
Publisher
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European Journal of Biochemistry
Date
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1993
1993-08
Subject
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Biochemistry & Molecular Biology; expression; cloning; dietary-cholesterol; purification; messenger-rna; circadian-rhythm; reductase; microsomes; sequence; serum-cholesterol
Creator
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Breuer O; Sudjanasugiaman E; Eggertsen G; Chiang J Y L; Bjorkhem I
Description
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Rats of the Sprague-Dawley strain were infused intravenously with a fat emulsion (Intralipid, trademark of Kabi Pharmacia, Uppsala, Sweden) containing 7-oxocholesterol. This resulted in an increased cholesterol 7alpha-hydroxylase activity in liver microsomes as compared to controls and was accompanied by increased levels of cholesterol 7alpha-hydroxylase mRNA and microsomal cholesterol 7alpha-hydroxylase protein. Rats were also fed a cholestyramine-supplemented diet and infused with 7-oxocholesterol. These animals excreted about half as much bile acids in faeces as cholestyramine-fed controls. Addition of 7-oxocholesterol to liver microsomes from normal rats in amounts corresponding to those present in microsomes from 7-oxocholesterol-treated rats inhibited the cholesterol 7alpha-hydroxylase activity by about 75%. Cholesterol induced a type-I binding spectrum when added to a purified bacterial-expressed cholesterol 7alpha-hydroxylase (P-450c7DELTA2-24). 7-Oxocholesterol competitively inhibited the cholesterol binding spectrum, while 7beta-hydroxycholesterol did not interfere with binding of cholesterol to the enzyme. It is concluded that treatment with the competitive inhibitor 7-oxocholesterol leads to a reduced bile acid biosynthesis and, as a consequence of reduced bile acid inhibition, a compensatory increase in cholesterol 7alpha-hydroxylase synthesis. The high enzyme activity measured in microsomal preparations from 7-oxocholesterol-treated rats may be due to a continuous conversion of 7-oxocholesterol into less inhibitory metabolites, e.g. 7beta-hydroxycholesterol. The latter compound was found in high concentrations in liver microsomes from rats treated with 7-oxocholesterol. The physiological importance of these results is discussed in relation to the previous findings that 7-oxocholesterol is accumulated in liver after cholesterol feeding and that 7-oxocholesterol is formed from cholesterol during lipid peroxidation.
Identifier
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<a href="http://doi.org/10.1111/j.1432-1033.1993.tb18082.x" target="_blank" rel="noreferrer noopener">10.1111/j.1432-1033.1993.tb18082.x</a>
Format
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Journal Article or Conference Abstract Publication
1993
Biochemistry & Molecular Biology
Bjorkhem I
Breuer O
Chiang J Y L
circadian-rhythm
Cloning
dietary-cholesterol
Eggertsen G
European Journal of Biochemistry
expression
Journal Article or Conference Abstract Publication
messenger-rna
Microsomes
purification
reductase
sequence
serum-cholesterol
Sudjanasugiaman E