Side chain hydroxylation of C27-steroids and vitamin D3 by a cytochrome P-450 enzyme system isolated from human liver mitochondria

Journal Article · Sun Nov 01 04:00:00 EST 1981 · J. Lipid Res.; (United States)

OSTI ID:5311310

Oftebro, H; Saarem, K; Bjoerkhem, I; Pedersen, J I

The present study was undertaken to obtain information on the involvement of cytochrome P-450 in the 26-hydroxylation on bile acid intermediates and in the 25-hydroxylation of vitamin D3 in human liver mitochondria. Cytochrome P-450 was solubilized from human liver mitochondria and purified two times to a specific content of 0.125 nmol per mg protein. Furthermore, a ferredoxin was isolated from the mitochondria and partly purified. This iron-sulfur protein had properties similar to bovine adrenal ferredoxin. A mitochondrial NADPH-ferredoxin reductase was also isolated and purified to homogeneity. This enzyme was a flavoprotein with properties very similar to the bovine adrenal NADPH-ferredoxin reductase. The cytochrome P-450 preparation catalyzed 26-hydroxylation of C27-steroids and 25-hydroxylation of vitamin D3 when reconstructed with NADPH, the ferredoxin and the ferredoxin reductase. With different substrates the following turnover numbers (nmol product X nmol P-450(-1) X min-1) were found: cholesterol, 8; 5-cholestene-3 beta, 7 alpha-diol, 10; 7 alpha-hydroxy-4-cholesten-3-one, 23; 7 alpha, 12 alpha-dihydroxy-4-cholesten-3-one, 27; 5 beta-cholestane-3 alpha, 7 alpha-diol, 28; 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol, 41; and vitamin D3, 0.16. The hydroxylation reactions were inhibited by CO and metyrapone. The human liver mitochondrial ferredoxin and ferredoxin reductase could be replaced by adrenal ferredoxin and adrenal ferredoxin reductase without reduction of activity, but they could not be replaced by microsomal NADPH-cytochrome P-450 reductase. It is concluded that human liver mitochondria contain cytochrome P-450 involved in the oxidation of the side chain of C27-steroids and vitamin D3.

• Research Organization: Institute for Nutrition Research, School of Medicine, University of Oslo, Norway
• OSTI ID: 5311310
• Journal Information: J. Lipid Res.; (United States), Journal Name: J. Lipid Res.; (United States) Vol. 22:8; ISSN JLPRA
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
551000 -- Physiological Systems
59 BASIC BIOLOGICAL SCIENCES
BILE ACIDS
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL PATHWAYS
BODY
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CYTOCHROMES
DIGESTIVE SYSTEM
FERREDOXIN
GLANDS
HYDROXY COMPOUNDS
HYDROXYLATION
KINETICS
LIVER
METALLOPROTEINS
MITOCHONDRIA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANOIDS
ORGANS
PHYSIOLOGY
PIGMENTS
PROTEINS
REACTION KINETICS
STEROIDS
STEROLS
SUBSTRATES
VITAMIN D
VITAMINS