The biochemistry of aromatic amines. 10. Enzymic N-hydroxylation of arylamines and conversion of arylhydroxylamines into o-aminophenols

Some aspects of the metabolism of urethane and N-hydroxyurethane in rodents

1. Urethane and N-hydroxyurethane are interconvertible in C(-) and C57 mice. 2. In newborn C57/DBA hybrid mice, prior treatment with 3-methylcholanthrene or urethane stimulated the N-hydroxylation of urethane; SKF 525A inhibited the N-hydroxylation at 24hr. but stimulated it at 48hr. after administration. 3. Liver homogenates of CBA and C3H mice, and of Chester Beatty and hooded rats, but not whole-body homogenates of 1-day-old C57/DBA mice or lung homogenate of 3-week-old Chester Beatty rats, metabolized urethane into N-hydroxyurethane in small but definite amounts. 4. Nitrite was detected in the bodies of newborn C57/DBA hybrid mice treated with lethal doses of urethane or N-hydroxyurethane; nitrite formation from N-hydroxyurethane was stimulated by pretreatment of the animals with 3-methylcholanthrene. 5. The rate of catabolism of N-hydroxyurethane by C57/DBA mice was faster in 8-day-old than in 1-day-old animals of the same sex, and faster in females than in males of the same age. 6. Liver slices of several species of rats and mice catabolized N-hydroxyurethane at rates that varied with the age and sex of animals of the same species; liver homogenates or microsomes were less effective than slices from the same liver. 7. The enzyme activity was destroyed by boiling or freezing the liver; it was inhibited by increasing substrate concentration and by urethane, n-butyl carbamate, cyanide, p-benzoquinone or 2,4-dinitrophenol, but not by p-chloromercuribenzoate or menadione. 8. The catabolism of N-hydroxyurethane by liver slices from adult H-strain rats was not oxygen-dependent. 9. Lung homogenates of 4-week-old female Chester Beatty rats catabolized N-hydroxyurethane at 40% of the rate of liver slices from the same source. 10. O-Acetyl- and O-ethoxycarbonyl-N-hydroxyurethane were rapidly deacylated by liver homogenates from adult hooded rats and adult C57 mice, and by human erythrocytes. 11. N-Hydroxyurethane reacted rapidly with pyridoxal phosphate at pH7.4 and 37 degrees . 12. The rate of decomposition of N-hydroxyurethane in 0.1 n-sodium hydroxide was increased by Ni(2+), Cu(2+), Mn(2+) and [Fe(CN)(6)](3-) and decreased by Cr(2+), Zn(2+), Co(2+), Mg(2+) and Fe(2+). 13. Attempts to synthesize sulphonates of N-hydroxyurethane gave ethyl hydrogen sulphate, probably via rearrangement of the unstable O-sulphonate.

The biochemistry of aromatic amines. The metabolism of 2-naphthylamine and 2-naphthylhydroxylamine derivatives

1. 2-Naphthylhydroxylamine and 2-nitrosonaphthalene were present in urine of dogs but not of guinea pigs, hamsters, rabbits or rats dosed with 2-naphthylamine. N-Acetyl-2-naphthylhydroxylamine and its O-sulphonic acid and O-glucosiduronic acid were not detected in the urine of any of these species. 2. Bile from rats dosed with 2-naphthylamine contained (2-naphthylamine N-glucosid)uronic acid and 6- and 5,6-substituted derivatives of 2-acetamidonaphthalene. 2-Amino-1-naphthyl and 2-acetamido-1-naphthyl derivatives, 2-naphthylhydroxylamine and its N-acetyl derivative or conjugates of these were not detected. Bile from a dog dosed with 2-naphthylamine contained no 2-amino-1-naphthyl derivatives. 3. 2-Naphthylhydroxylamine was metabolized by the dog, rat and guinea pig to the same products as those formed by these species from 2-naphthylamine. Rabbits formed mainly 2-amino-1-naphthyl derivatives; these are minor metabolites of 2-naphthylamine in this species. 4. (N-Acetyl-2-naphthylhydroxylamine O-glucosid)uronic acid was excreted in the urine and the bile of rats and in the urine of guinea pigs and rabbits dosed with N-acetyl-2-naphthylhydroxylamine. 5. After the administration of 2-acetamidonaphthalene, (N-acetyl-2-naphthylhydroxylamine O-glucosid)uronic acid was detected in the urine of dogs, but not in the urine of other species. The dog excreted an acid-labile cysteine derivative of 2-acetamidonaphthalene, but only traces of the corresponding mercapturic acid. 6. After dosing with N-acetyl-2-naphthylhydroxylamine-O-sulphonic acid, rats excreted derivatives of 2-amino-1-naphthol. 7. 2-Nitrosonaphthalene, N-acetyl-2-naphthylhydroxylamine, N-acetyl-2-naphthylhydroxylamine-O-sulphonic acid, 2-naphthylhydroxylamine-N-sulphonic acid, N-benzyloxycarbonyl-2-naphthylhydroxylamine and N-benzyloxycarbonyl-2-naphthylhydroxylamine-O-sulphonic acid were synthesized.

Acetyl transfer in arylamine metabolism

1. N-Hydroxyacetamidoaryl compounds (hydroxamic acids) are metabolites of arylamides, and an enzyme that transfers the acetyl group from these derivatives to arylamines has been found in rat tissues. The reaction products were identified by thin-layer chromatography and a spectrophotometric method, with 4-amino-azobenzene as acetyl acceptor, was used to measure enzyme activity. 2. The acetyltransferase was in the soluble fraction of rat liver, required a thiol for maximum activity and had a pH optimum between 6.0 and 7.5. 3. The soluble fractions of various rat tissues showed decreasing activity in the following order: liver, adrenal, kidney, lung, spleen, testis, heart; brain was inactive. 4. With the exception of aniline and aniline derivatives all the arylamines tested were effective as acetyl acceptors but aromatic compounds with side-chain amino groups were inactive. 5. The N-hydroxyacetamido derivatives of 2-naphthylamine, 4-amino-biphenyl and 2-aminofluorene were active acetyl donors but N-hydroxyacetanilide showed only slight activity. Acetyl-CoA was not a donor. 6. Some properties of the enzyme are compared with those of other acetyltransferases.