Oxidation of uroporphyrinogen by methylcholanthrene-induced cytochrome P-450. Essential role of cytochrome P-450d.
We have previously shown that uroporphyrinogen is oxidized to uroporphyrin by microsomes (microsomal fractions) from 3-methylcholanthrene-pretreated chick embryo liver [Sinclair, Lambrecht & Sinclair (1987) Biochem. Biophys. Res. Commun. 146, 1324-1329]. We report here that a specific antibody to chick liver methylcholanthrene-induced cytochrome P-450 (P-450) inhibited both uroporphyrinogen oxidation and ethoxyresorufin O-de-ethylation in chick-embryo liver microsomes. 3-Methylcholanthrene-pretreatment of rats and mice markedly increased uroporphyrinogen oxidation in hepatic microsomes as well as P-450-mediated ethoxyresorufin de-ethylation. In rodent microsomes, uroporphyrinogen oxidation required the addition of NADPH, whereas chick liver microsomes required both NADPH and 3,3',4,4'-tetrachlorobiphenyl. Treatment of rats with methylcholanthrene, hexachlorobenzene and o-aminoazotoluene increased uroporphyrinogen oxidation and P-450d, whereas phenobarbital did not increase either. The contribution of hepatic P-450c and P-450d to uroporphyrinogen oxidation and ethoxyresorufin O-de-ethylation in methylcholanthrene-induced microsomes was assessed by using specific antibodies to P-450c and P-450d. Uroporphyrinogen oxidation by methylcholanthrene-induced rat liver microsomes was inhibited up to 75% by specific antibodies to P-450d, but not by specific antibodies to P-450c. In contrast, ethoxyresorufin de-ethylation was inhibited only 20% by anti-P450d but 70% by anti-P450c. Methylcholanthrene-induced kidney microsomes which contain P-450c but non P-450d did not oxidize uroporphyrinogen. These data indicate that hepatic P-450d catalyses uroporphyrinogen oxidation. We suggest that the P-450d-catalysed oxidation of uroporphyrinogen has a role in the uroporphyria caused by hexachlorobenzene and other compounds.
Jacobs
J M
JM
Department of Pharmacology, Dartmouth Medical School, Hanover, NH 03756.
Sinclair
P R
PR
Bement
W J
WJ
Lambrecht
R W
RW
Sinclair
J F
JF
Goldstein
J A
JA
D000818:Animals; D000906:Antibodies / Q000276:immunology; D002642:Chick Embryo; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005260:Female; D006581:Hexachlorobenzene / Q000494:pharmacology; D015151:Immunoblotting; D007668:Kidney / Q000378:metabolism; D008748:Methylcholanthrene; D008862:Microsomes, Liver / Q000378:metabolism*; D010078:Oxazines / Q000494:pharmacology; D010084:Oxidation-Reduction; D010634:Phenobarbital / Q000494:pharmacology; D011165:Porphyrinogens / Q000378:metabolism*; D051381:Rats; D014577:Uroporphyrinogens / Q000378:metabolism*; D009762:o-Aminoazotoluene / Q000494:pharmacology
D000906:Antibodies; D010078:Oxazines; D011165:Porphyrinogens; D014577:Uroporphyrinogens; D006581:Hexachlorobenzene; D008748:Methylcholanthrene; C007649:ethoxyresorufin; D003577:Cytochrome P-450 Enzyme System; D009762:o-Aminoazotoluene; D010634:Phenobarbital