TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is a tight binding inhibitor of cytochrome P-450d.
Based on data indicating that compounds which induce cytochrome P-450d also bind to the enzyme [R. Voorman and S. D. Aust (1987). Toxicol. Appl. Pharmacol. 90, 69-78], we investigated the inhibition of cytochrome P-450d-dependent estradiol 2-hydroxylase by (2,3,7,8-tetrachlorodibenzo-p-dioxin TCDD), using ligand-free cytochrome P-450d from isosafrole-treated rats. Since maximum inhibition of estradiol 2-hydroxylase occurred at TCDD concentrations comparable to the concentration of enzyme (50 nM), a modified form of steady-state kinetic analysis was used. Using I50 = Et/2 + Ki where Et = total enzyme concentration), we showed that TCDD inhibited cytochrome P-450d-dependent estradiol 2-hydroxylase activity with Ki equal to 8 nM. Association of TCDD with P-450d occurred within 2 min of inhibitor addition. Therefore, TCDD can be considered a tight binding inhibitor of cytochrome P-450d.
Voorman
R
R
Department of Biochemistry, Michigan State University, East Lansing 48824.
Aust
S D
SD
D000818:Animals; D019363:Cytochrome P-450 CYP1A1; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification / Q000378:metabolism; D004147:Dioxins / Q000494:pharmacology*; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000037:antagonists & inhibitors* / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D008297:Male; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors
D065607:Cytochrome P-450 Enzyme Inhibitors; D004147:Dioxins; D007527:Isoenzymes; D000072317:Polychlorinated Dibenzodioxins; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D019363:Cytochrome P-450 CYP1A1; C020120:estrogen 2-hydroxylase