Evidence that arylhydroxamic acid N,O-acyltransferase and the genetically polymorphic N-acetyltransferase are properties of the same enzyme in rabbit liver.

Glowinski, Irene B.; Weber, Wendell W.; Fysh, Jacquelene M.; Vaught, Jimmie B.; King, Charles M.

doi:10.1016/s0021-9258(19)43917-3

Cited by 54 publications

(5 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Evidence that the cofactor-independent conversion of carcinogenic N-arylhydroxamic acids to electrophilic reactants in mammalian cell cytosols involves the formation of reactive N-acetoxyarylamines was reported in 1972 (36). Subsequently, it was established that the cytosolic transformation of N-arylhydroxamic acids to N-acetoxyarylamines via N,O-acyl transfer is catalyzed by NATs (37). We found that both hamster NAT1 and NAT2 undergo pseudo-first-order, self-catalyzed irreversible inactivation in the presence of N-OH-AAF and, more recently, we determined that the reactive product responsible for the inactivation of hamster NAT1 by N-OH-AAF is 2-nitrosofluorene (17,20,21).…”

Section: Discussionmentioning

confidence: 99%

Irreversible Inactivation of Arylamine N-Acetyltransferases in the Presence of N-Hydroxy-4-Acetylaminobiphenyl: A Comparison of Human and Hamster Enzymes

Wang

Wagner

Hanna

2005

Chem. Res. Toxicol.

View full text Add to dashboard Cite

Arylamine N-acetyltransferases (NATs) catalyze the N-acetylation of arylamines, the O-acetylation of N-arylhydroxylamines, and the conversion of N-(aryl)acetohydroxamic acids to N-acetoxyarylamines. NATs also undergo irreversible inactivation in the presence of N-(aryl)acetohydroxamic acids. We previously established that inactivation of hamster NAT1 by N-hydroxy-2-acetylaminofluorene is the result of sulfinamide adduct formation with Cys68. The purpose of this research was to determine the kinetics of inactivation of hamster NAT1, hamster NAT2, and human NAT1 by N-hydroxy-4-acetylaminobiphenyl (N-OH-4-AABP), to identify the amino acids that are modified upon NAT-catalyzed bioactivation of N-OH-4-AABP, to characterize the adducts and to identify factors that influence the propensity of NATs to undergo inactivation by N-arylhydroxamic acids. Mass spectrometric analysis of the NATs, after incubation with N-OH-4-AABP, revealed that the principal adduct of each protein was a (4-biphenyl)sulfinamide. Proteolysis of the adducted NATs caused hydrolysis of the sulfinamides to sulfinic acids. Tandem mass spectrometric analysis of the modified peptides revealed that each NAT isozyme contained a sulfinic acid on the Cys68 side chain. Minor adducts were identified as 4-aminobiphenyl conjugates of tyrosines. Hamster NAT1 was more rapidly inactivated by N-OH-4-AABP than either hamster NAT2 or human NAT1, and it was demonstrated that 4-nitrosoobiphenyl, which forms the sulfinamide adducts, accumulates during incubation of N-OH-4-AABP with hamster NAT2 and human NAT1 but not during incubations with hamster NAT1. Steady state kinetic analysis of the hydrolysis of acetylated NATs revealed that the half-lives of acetylated hamster NAT2 and human NAT1 are 7-8-fold greater than that of acetylated hamster NAT1. These results support the proposal that the mechanism of inactivation of NATs by N-OH-4-AABP involves initial deacetylation to produce N-OH-4-aminobiphenyl, which after oxidative conversion to 4-nitrosobiphenyl reacts with Cys68 to form a sulfinamide. The relatively short half-life of the acetylated form of hamster NAT1 contributes to its greater susceptibility to inactivation by N-OH-4-AABP.

show abstract

Section: Discussionmentioning

confidence: 99%

Irreversible Inactivation of Arylamine N-Acetyltransferases in the Presence of N-Hydroxy-4-Acetylaminobiphenyl: A Comparison of Human and Hamster Enzymes

Wang

Wagner

Hanna

2005

Chem. Res. Toxicol.

View full text Add to dashboard Cite

show abstract

“…JV-(Deoxyguanosin-8-yl)-7-fluoro-2-acetamidofluorene (23). Compound 23 was prepared from 10 by the method described above for the synthesis of 22: yield 30%; recrystallized from EtOH-H20; mp above 200 °C dec; 13C NMR (Me2SO-d6, 62.9 MHz) tabulated in the supplementary material.…”

Section: -Substituted 2-(at-acetoxyacetamido)fluorenes (9-13)mentioning

confidence: 99%

“…In addition, AHAT has received considerable attention because of its potential relevance to carcinogenic and mutagenic processes and because it appears to be identical with certain forms of an important drug metabolizing enzyme, acetylcoenzyme A: arylamine N-acetyltransferase (EC 2.3.1.5). 23,24 Only limited information is available regarding the influence of aromatic ring substituents on the reactivity or fate of activated forms of N-arylhydroxamic acids. Kriek and Hengeveld found that the potassium salt of 4-[(Nsulfonoxy)acetamido]-4,-fluorobiphenyl is at least twice as reactive toward methionine and guanosine as the 4'-H compound.…”

mentioning

confidence: 99%

Substituent effects on the bioactivation of 2-(N-hydroxyacetamido)fluorenes by N-arylhydroxamic acid N,O-acyltransferase

Elfarra¹,

Hanna²

1985

J. Med. Chem.

View full text Add to dashboard Cite

A series of 7-substituted analogues of 2-(N-hydroxyacetamido)fluorene (1) was subjected to bioactivation by a partially purified preparation of hamster hepatic AHAT, and the rates of methylthio adduct formation resulting from the reaction of the activated intermediates with N-acetylmethionine were determined. Electronegative substituents enhanced the amount of adduct formed; this finding contrasted with the results of a previous study in which it was found that electron-donating substituents facilitated the mechanism-based inactivation of AHAT by analogues of 1. The structures of the adducts formed from reaction of the activated forms of several of the 7-substituted compounds with N-acetylmethionine and with 2'-deoxyguanosine were determined; the types of adducts formed were similar to those formed with electrophiles generated by the AHAT-catalyzed activation of 1. Electronegative substituents enhanced the amount of adducts formed in the reaction with 2'-deoxyguanosine as well as with N-acetylmethionine.

show abstract

“…N-Acetylation of the monoamino arylamines to which humans are commonly exposed is considered a detoxification reaction because acetylation decreases substrate availability for metabolic hydroxylation of the primary amino group, a process that frequently leads to the production of toxic and/or carcinogenic N -arylhydroxylamines (ArNHOH) , . NATs also catalyze the formation of N -acetoxyarylamines (ArNHOCOCH 3 ) by O-acetylation of N -arylhydroxylamines and by using N -arylhydroxamic acids (ArNOHCOCH 3 ) as substrates in an AcCoA-independent N , O -acetyl transfer reaction – . N -Acetoxyarylamines are unstable, electrophilic molecules that form covalent bonds with nucleophilic functional groups on DNA and are believed to be responsible, at least in part, for initiation of arylamine-induced carcinogenesis .…”

Section: Introductionmentioning

confidence: 99%

Arylamine N-Acetyltransferases: Characterization of the Substrate Specificities and Molecular Interactions of Environmental Arylamines with Human NAT1 and NAT2

Liu

Vett

Zhang

et al. 2007

Chem. Res. Toxicol.

View full text Add to dashboard Cite

Arylamine N-acetyltransferases (NATs) are phase II xenobiotic metabolism enzymes that catalyze the detoxification of arylamines by N-acetylation and the bioactivation of N-arylhydroxylamines by O-acetylation. Endogenous and recombinant mammalian NATs with high specific activities are difficult to obtain in substantial quantities and in a state of homogeneity. This paper describes the overexpression of human wild-type NAT2 as a dihydrofolate reductase fusion protein containing a TEV protease-sensitive linker. Treatment of the partially purified fusion protein with TEV protease, followed by chromatographic purification, afforded 2.8 mg of homogeneous NAT2 from 2 L of cell culture. The kinetic specificity constants ( k cat/ K m) for N-acetylation of arylamine environmental contaminants, some of which are associated with bladder cancer risk, were determined with NAT2 and NAT1. The NAT1/NAT2 ratio of the specificity constants varied almost 1000-fold for monosubstituted and disubstituted alkylanilines containing methyl and ethyl ring substituents. 2-Alkyl substituents depressed N-acetylation rates but were more detrimental to catalysis by NAT1 than by NAT2. 3-Alkyl groups caused substrates to be preferentially N-acetylated by NAT2, and both 4-methyl- and 4-ethylaniline were better substrates for NAT1 than NAT2. NMR-based models were used to analyze the NAT binding site interactions of the alkylanilines. The selectivity of NAT1 for acetylation of 4-alkylanilines appears to be due to binding of the substituents to V216, which is replaced by S216 in NAT2. The contribution of 3-alkyl substituents to NAT2 substrate selectivity is attributed to multiple bonding interactions with F93, whereas a single bonding interaction occurs with V93 in NAT1. Unfavorable steric clashes between 2-methyl substituents and F125 of NAT1 may account for the selective NAT2-mediated N-acetylation of 2-alkylanilines; F125 is replaced by S125 in NAT2. These results provide insight into the structural basis for the substrate specificity of two NATs that play major roles in the biotransformation of genotoxic environmental arylamines.

show abstract

Evidence that arylhydroxamic acid N,O-acyltransferase and the genetically polymorphic N-acetyltransferase are properties of the same enzyme in rabbit liver.

Cited by 54 publications

References 22 publications

Irreversible Inactivation of Arylamine N-Acetyltransferases in the Presence of N-Hydroxy-4-Acetylaminobiphenyl: A Comparison of Human and Hamster Enzymes

Irreversible Inactivation of Arylamine N-Acetyltransferases in the Presence of N-Hydroxy-4-Acetylaminobiphenyl: A Comparison of Human and Hamster Enzymes

Substituent effects on the bioactivation of 2-(N-hydroxyacetamido)fluorenes by N-arylhydroxamic acid N,O-acyltransferase

Arylamine N-Acetyltransferases: Characterization of the Substrate Specificities and Molecular Interactions of Environmental Arylamines with Human NAT1 and NAT2

Contact Info

Product

Resources

About