title: Evidence for peroxisomal hydroxylase activity in rat liver.
abstract: This study presents evidence for the first time that rat liver peroxisomes contain a hydroxylase capable of converting 3 alpha, 7 alpha, 12 alpha,- trihydroxy-5 beta-cholestane to a cholestanetetrol. Furthermore, this hydroxylase differs from both the mitochondrial and microsomal enzymes in its response to various co-factors. Highly purified peroxisomal, mitochondrial, and microsomal fractions from cholestryamine-treated rats were incubated with [22(23)-3H]3 alpha,7 alpha,12 alpha,-trihydroxy-5 beta-cholestane under a variety of conditions. The products were acidified, extracted, and subjected to thin-layer chromatography to determine the amount of cholestanetetrol produced. The identification of the 25- and 26-hydroxylated products from the incubations with the microsomes was confirmed by gas chromatography-mass spectrometry. Peroxisomal fractions incubated with a NADPH-generating system, Mg2+, and ATP showed a rate of 40 pmol/min/mg conversion of 3 alpha,7 alpha,12 alpha,-trihydroxy-5 beta-cholestane to a cholestanetetrol. Co-factor studies indicated that both the peroxisomal and mitochondrial hydroxylase activities were dependent on NADPH, Mg2+, and ATP (with different concentration requirements) whereas the microsomal hydroxylase(s) required only NADPH. An abstract of this work has been published (1).
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002777:Cholestanols / Q000378:metabolism; D002793:Cholic Acids / Q000378:metabolism; D008099:Liver / Q000201:enzymology / Q000648:ultrastructure*; D008274:Magnesium / Q000378:metabolism; D008297:Male; D008830:Microbodies / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D008930:Mitochondria, Liver / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000032:analysis*; D009249:NADP / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D002777:Cholestanols; D002793:Cholic Acids; D009249:NADP; C037469:3,7,12,25-tetrahydroxycholestan-24-one; C003681:3,7,12-trihydroxycoprostanic acid; D000255:Adenosine Triphosphate; D006899:Mixed Function Oxygenases; D008274:Magnesium