US EPA

5363665 

Journal Article 

1,2-Naphthalene Oxide As An Intermediate In The Microsomal Hydroxylation Naphthalene 

Jerina, DM; Daly, JW; Witkop, B; Zaltzman-Nirenberg, P; Udenfriend, S 

1970 

Yes 

Biochemistry
ISSN: 0006-2960
EISSN: 1520-4995 

9 

1 

The microsomal metabolism of naphthalene (91203) was investigated in rats and rabbits. Rat liver microsomes were prepared from animals which had received intraperitoneal injections of phenobarbital (50066) (40 milligrams per kilogram) for 4 days. Rat liver microsomes or rabbit liver microsomes from untreated rabbits were incubated with 4 micromoles of naphthalene and production of naphthol and trans-1,2-dihydro-1,2-dihydroxynaphthalene (dihydrodiol) was estimated colorimetrically. Carbon-14 (C-14) labeled naphthalene was also used as substrate with the addition of 0.5 milliliters (ml) of a 0.06 molar (M) solution of glutathione (GSH) and the isolated GSH conjugate was assayed radiometrically. Conjugation of GSH with 1,2-naphthalene-oxide (17180880) was also examined under enzymatic and nonenzymatic conditions. Rabbit liver homogenates were incubated with 3mg racemic 1,2-naphthalene-oxide together with oxygen-18 (O-18) and O-18-dihydrodiol estimated. Naphthalene incubation with or without styrene-oxide as a cosubstrate for epoxide-hydrase was examined. Incubations of naphthalene with liver microsomes from phenobarbital induced rats produced 12 to 15 percent 2-napthol (135193), the remainder being 1-naphthol (90153). Normal rabbit liver microsomes formed only 1 to 3 percent 2-naphthol. With rabbit liver microsomes, dihydrodiol was formed both with naphthalene and with naphthalene-oxide as substrates. After naphthalene-oxide incubation with O-18 enriched water, the isolated dihydrodiol contained 45 percent O-18. Dehydration of the dihydrodiol produced 1-naphthol with less than 1 percent O-18 and 2-naphthol with 39 percent O-18. Incubation of naphthalene with GSH yielded a GSH conjugate, S-(1,2-dihydro-2-hydroxynaphthyl)-glutathione, along with naphthol and dihydrodiol. When increasing amounts of GSH were added, the amount of the GSH conjugate increased at the expense of naphthol and dihydrodiol. The same GSH conjugate was formed by addition of GSH to 1,2-naphthalene-oxide under both conditions. When competitive substrate for the epoxide-hydrase was added, the yield of naphthol increased and the dihydrodiol decreased. The authors conclude that 1,2-naphthalene-oxide is a necessary precursor for all naphthalene metabolites.