title: Assay method for mitochondrial sterol 27-hydroxylase with 7alpha-hydroxy-4-cholesten-3-one as a substrate in the rat liver.
abstract: Mitochondrial sterol 27-hydroxylase (EC 1.14.13.15) is an important enzyme, not only in the formation of bile acids from cholesterol intermediates in the liver but also in the removal of cholesterol by side chain hydroxylation in extrahepatic tissues. The enzyme has been assayed by complicated methods using radiolabeled substrates or deuterium-labeled tracers. These methods may be inaccurate for measuring enzyme activity, because the amount of electron-transferring proteins may be insufficient for maximal velocity. To solve this problem, after solubilization of the enzyme from rat liver mitochondria with n-octyl-beta-d-glucopyranoside (OGP), we measured the enzyme activity by incubating the solubilized enzyme with saturated amounts of electron-transferring proteins. In our assay system, using 7alpha-hydroxy-4-cholesten-3-one (HCO) as a substrate, we could easily measure the product, 7alpha,27-dihydroxy-4-cholesten-3-one, with HPLC monitoring absorbance at 240 nm. The product formation was proportionate to the time up to 5 min and the protein concentration up to 0.5 mg of protein/ml. The maximal velocity of the enzyme was 1.1 nmol/min/mg of protein, which was 4- to 16-fold higher than previously reported values. A simple and accurate assay method for sterol 27-hydroxylase in rat liver mitochondria is herein described.
authors.affiliation: Department of Surgery I, Miyazaki Medical College, 5200 Kihara, Kiyotake, Miyazaki 889-1692, Japan.
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ota
authors.forename: Tada-Aki
authors.initials: TA
authors.lastname: Eto
authors.forename: Shun-Ichi
authors.initials: S
authors.lastname: Tanaka
authors.forename: Hideto
authors.initials: H
authors.lastname: Sueta
authors.forename: Hironori
authors.initials: H
authors.lastname: Shiotsuki
authors.forename: Yorio
authors.initials: Y
authors.lastname: Maeda
authors.forename: Mizuho
authors.initials: M
authors.lastname: Une
authors.forename: Kazuo
authors.initials: K
authors.lastname: Chijiiwa
mesh_terms: D000818:Animals; D053493:Cholestanetriol 26-Monooxygenase; D002783:Cholestenones / Q000378:metabolism*; D004579:Electron Transport; D005260:Female; D006900:Hydroxylation; D008930:Mitochondria, Liver / Q000201:enzymology* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013379:Substrate Specificity; D013696:Temperature; D013997:Time Factors
chemical_list: D002783:Cholestenones; C002656:7 alpha-hydroxy-4-cholesten-3-one; D013250:Steroid Hydroxylases; D053493:Cholestanetriol 26-Monooxygenase