title: Comparison of 12alpha-hydroxylation of oxygenated 5alpha-cholestanes and allochenodeoxycholate with rat liver microsomes.
abstract: [5alpha,6alpha-3H2]-5alpha-Cholestane-3alpha,7alpha-diol (A), (25 R)-3alpha,7alpha-dihydroxyl-[5alpha,6alpha-3H2]-5alpha--cholestan-26-oic acid (B),(25R)-[5alpha,6alpha-3H2]stane-3alpha,7alpha-26-triol (C), and [3beta-3H]allochenodeoxycholic acid (D) were prepared, characterized, and studied with a rat liver microsomal preparation fortified with 1 mM NADPH. The 12alpha-hydroxylated product formed from each of these substrates was identified by isotopic dilution; the relative reactivity of the four substrates was (A) 100; (B) 87; (C) 135; and (D) 40. The microsomal system showed a requirement for added NADPH and other properties similar to those shown for 12alpha-hydroxylation of 7alpha-hydroxycholest-4-en-3-one, which is ultimately converted to cholic acid. Since the coplanar 5alpha-cholestane-3alpha,7alpha-diol is virtually superimposable upon 7alpha-hydroxycholest-4-en-3-one, and the enzymic requirements are comparable, it is suggested that a single enzyme system may be responsible for 12alpha-hydroxylation of these substrates.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002635:Chenodeoxycholic Acid / Q000031:analogs & derivatives / Q000378:metabolism*; D002776:Cholestanes / Q000378:metabolism*; D004492:Edetic Acid / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000201:enzymology; D010084:Oxidation-Reduction; D011485:Protein Binding; D051381:Rats; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013997:Time Factors
chemical_list: D002776:Cholestanes; D002635:Chenodeoxycholic Acid; D004492:Edetic Acid; D013250:Steroid Hydroxylases; D008274:Magnesium