title: Purification and characterization of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol 27-hydroxylase from female rat liver mitochondria.
abstract: 5 beta-Cholestane-3 alpha,7 alpha,12 alpha-triol 27-hydroxylase (5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol, NADPH:oxygen oxidoreductase (26-hydroxylating), EC 1.14.13.15) was purified from female rat liver mitochondria based on its catalytic activity. The final preparation of the enzyme showed a single major band on the sodium dodecyl sulfate-polyacrylamide gel electrophoretogram. The content of purified enzyme was 12 nmol/mg of protein, and the specific activity was 431 nmol/min/mg of protein. The molecular weight of the enzyme was determined from sodium dodecyl sulfate-polyacrylamide gel electrophoresis as 52,500. The absorption spectra of the purified enzyme and that of the dithionite-reduced CO complex showed peaks at 417 and 450 nm, respectively, indicating the enzyme belongs to the cytochrome P-450 family. Upon reconstitution with the electron-transferring system of the adrenal (adrenodoxin and NADPH-adrenodoxin reductase), the enzyme showed high activity hydroxylating 5 beta-cholestane-3 alpha,7 alpha-12-triol at position 27 with a turnover number of 35.5 min-1 and Km of 6.3 microM. The enzyme activity was completely lost when the electron-transferring system was replaced by that of microsomes (NADPH-cytochrome P-450 reductase purified from rat liver microsomes), confirming that the P-450 enzyme was of the mitochondrial type, but not of the microsomal. The omission of cytochrome P-450, adrenodoxin, or NADPH-adrenodoxin reductase resulted in complete loss of enzyme activity. The specific activity toward 5 beta-cholestane-3 alpha, 7 alpha-diol was less than one-half that toward cholestanetriol and that toward cholesterol was about one-fiftieth. The enzyme showed no activity toward xenobiotics such as benzphetamine, 7-ethoxycoumarin, and benzo[a]pyrene. Its activity was not inhibited by metyrapone and slightly inhibited by aminoglutethimide. The enzyme activity was markedly lowered in an atmosphere of CO/O2/N2, 40/20/40.
authors.affiliation: Department of Biochemistry, Hiroshima University School of Dentistry, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Okuda
authors.forename: O
authors.initials: O
authors.lastname: Masumoto
authors.forename: Y
authors.initials: Y
authors.lastname: Ohyama
mesh_terms: D000818:Animals; D053493:Cholestanetriol 26-Monooxygenase; D002845:Chromatography; D002852:Chromatography, Ion Exchange; D017886:Durapatite; D005260:Female; D006882:Hydroxyapatites; D007700:Kinetics; D008930:Mitochondria, Liver / Q000201:enzymology*; D008970:Molecular Weight; D051381:Rats; D011919:Rats, Inbred Strains; D013250:Steroid Hydroxylases / Q000302:isolation & purification* / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D006882:Hydroxyapatites; D017886:Durapatite; D013250:Steroid Hydroxylases; D053493:Cholestanetriol 26-Monooxygenase