Differential effect of copper (II) on the cytochrome P450 enzymes and NADPH-cytochrome P450 reductase: inhibition of cytochrome P450-catalyzed reactions by copper (II) ion.
Inhibitory effects of Cu(2+) on the cytochrome P450 (P450)-catalyzed reactions of liver microsomes and reconstituted systems containing purified P450 and NADPH-P450 reductase (NPR) were seen. However, Zn(2+), Mg(2+), Mn(2+), Ca(2+), and Co(2+) had no apparent effects on the activities of microsomal P450s. Cu(2+) inhibited the reactions catalyzed by purified P450s 1A2 and 3A4 with IC(50) values of 5.7 and 8.4 microM, respectively. Cu(2+) also inhibited reduction of cytochrome c by NPR (IC(50) value of 5.8 microM). Copper caused a decrease in semiquinone levels of NPR, although it did not disturb the rate of formation of semiquinone. P450 reactions supported by an oxygen surrogate, tert-butyl hydroperoxide, instead of NPR and NADPH, were inhibited by the presence of Cu(2+). The results indicate that Cu(2+) inhibits the P450-catalyzed reactions by affecting both P450s and NPR. It was also found that the inhibition of catalytic activities of P450s by Cu(2+) involves overall conformational changes of P450s and NPR, investigated by CD and intrinsic fluorescence spectroscopy. These results suggest that the inhibitory effect of Cu(2+) on the P450-catalyzed reactions may come from the inability of an efficient electron transfer from NPR to P450 and also the dysfunctional conformation of NPR and P450.
AngioLab, Pai-Chai University, Taejon 302-735, Republic of Korea.
Joon-Sik
JS
Kim
Taeho
T
Ahn
Sung-Kun
SK
Yim
Chul-Ho
CH
Yun
D000818:Animals; D002384:Catalysis; D002942:Circular Dichroism; D003300:Copper / Q000494:pharmacology*; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology; D009249:NADP / Q000378:metabolism; D009251:NADPH-Ferrihemoprotein Reductase / Q000037:antagonists & inhibitors*; D010084:Oxidation-Reduction; D011817:Rabbits; D013056:Spectrophotometry, Ultraviolet
D065607:Cytochrome P-450 Enzyme Inhibitors; D009249:NADP; D003300:Copper; D003577:Cytochrome P-450 Enzyme System; D006861:Hydrogen Peroxide; D009251:NADPH-Ferrihemoprotein Reductase