Kinetics of inhibition of estrogen 2-hydroxylase by various haloestrogens

Journal Article · Fri Jul 01 04:00:00 EDT 1983 · Steroids; (United States)

DOI:https://doi.org/10.1016/S0039-128X(83)90120-4· OSTI ID:7008180

Brueggemeier, R W; Kimball, J G

Inhibitors of estrogen 2-hydroxylase can be utilized in studying the kinetics of this cytochrome P450 enzyme complex and in elucidating the structural requirements of the active site. The conversion of estrogens to 2-hydroxyestrogens in rat liver microsomal preparations was examined using two radiotracer assays, the conversion of (4-/sup 14/C)-estradiol to (4-/sup 14/C)-2-hydroxyestradiol and the release of /sup 3/H/sub 2/O from (2-/sup 3/H)-estradiol. Using the microsomal fraction from male rat liver, the apparent K/sub m/ for the substrate estradiol was 2.2 microM. Competitive inhibition was observed for 2-halo- and 2,4-haloestrogens (apparent K/sub i/'s of 1.6 to 3.7 microM), while 4-haloestrogens did not produce normal inhibition patterns. Employing female rat liver microsomes in which nonclassical enzyme kinetics was observed, the synthetic steroids increased the sigmoidal character of the velocity curve. Multiple inhibition studies with 2-haloestrogens and 4-haloestrogens with the male rat liver microsomal fraction indicated that these compounds are mutually exclusive inhibitors of the 2-hydroxylase activity.

• Research Organization: College of Pharmacy, Ohio State University, Columbus
• OSTI ID: 7008180
• Journal Information: Steroids; (United States), Journal Name: Steroids; (United States) Vol. 42:1; ISSN STEDA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ANIMALS
BIOCHEMICAL REACTION KINETICS
BODY
CARBON 14 COMPOUNDS
DIGESTIVE SYSTEM
ENZYME INHIBITORS
ENZYMES
ESTROGENS
GLANDS
HORMONES
HYDROXYLASES
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
LIVER
MAMMALS
METABOLISM
ORGANS
OXIDOREDUCTASES
RATS
REACTION KINETICS
RODENTS
STEROID HORMONES
STRUCTURE-ACTIVITY RELATIONSHIPS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
VERTEBRATES