title: 7 alpha-hydroxylation of 27-hydroxycholesterol in human liver microsomes.
abstract: Human liver microsomes were found to catalyze 7 alpha-hydroxylation of 27-hydroxycholesterol at a rate of up to about 0.2 nmol/mg protein per min. The product of the reaction, 5-cholestene-3 beta, 7 alpha, 27-triol, was identified by means of combined gas chromatography-mass spectrometry. Liver microsomes from two patients with an upregulated cholesterol 7 alpha-hydroxylase, did not have higher 7 alpha-hydroxylase activity towards 27-hydroxycholesterol than those from untreated patients, suggesting that the 7 alpha-hydroxylase active towards 27-hydroxycholesterol is not the same as that active towards cholesterol. The mitochondrial fraction of liver from untreated patients and patients treated with cholestyramine, had negligible 7 alpha-hydroxylase activity towards 27-hydroxycholesterol less than 0.01 nmol/mg protein per min). The results are in accord with the possibility that there is a pathway to bile acids in human liver in which the first step is a 27-hydroxylation of cholesterol.
authors.affiliation: Department of Clinical Chemistry, Karolinska Institutet, Huddinge Hospital, Sweden.
authors.forename: I
authors.initials: I
authors.lastname: Björkhem
authors.forename: B
authors.initials: B
authors.lastname: Nyberg
authors.forename: K
authors.initials: K
authors.lastname: Einarsson
mesh_terms: D000328:Adult; D000368:Aged; D002855:Chromatography, Thin Layer; D005260:Female; D006801:Humans; D006888:Hydroxycholesterols / Q000378:metabolism*; D006900:Hydroxylation; D008297:Male; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism*; D008875:Middle Aged; D008930:Mitochondria, Liver / Q000378:metabolism*; D014316:Tritium
chemical_list: D006888:Hydroxycholesterols; D014316:Tritium; C076996:27-hydroxycholesterol