Monomorphic and polymorphic isozymes of arylamine N-acetyltransferases inhamster liver: purification of the isozymes and genetic basis of N-acetylation polymorphism

Abstract

Two forms of cytosolic acetyltransferases, AT-I and AT-II, have been purified from hamster livers, and a comparison made of their chemical and catalytic properties and genetically expressed difference. Homogeneous AT-I and AT-II were 31 and 30 kd respectively on SDS-PAGE and catalyzed efficiently various N- and O-acetylations in their reconstitution systems. AT-I used both acetyl CoA and arylhydroxamic acids as acetyl donors, while AT-II did not utilize arylhydroxamic acids as acetyl donors. In the reconstitution system, purified AT-I, but not AT-II, catalyzed acetyl CoA-dependent O-acetylation of 2-N-hydroxyamino-6-methyldipyrido[1,2-alpha:3', 2'-d]imidazole (N-OH-Glu-P-1) and arylhydroxamic acid-dependent N-acetylation of 4-aminoazobenzene (AAB). On the other hand purified AT-II showed high activities of acetyl CoA-dependent N-acetylation of 2-aminofluorene (AF) and p-aminobenzoic acid (PABA). Polyclonal antibodies raised against AT-I inhibited cytosolic acetylations of N-OH-Glu-P-1 and AAB, and to a lesser extent of AF, while PABA N-acetylation was only marginally inhibited. Using Western blots, both AT-I and AT-II were recognized by the antibodies. AT-I was detectable in all the livers examined, and the content did not differ among the individuals (monomorphic distribution). In contrast, AT-II was distributed polymorphically, and the trimodal distribution of AT-II (high, intermediate and low) was correlated with the phenotype identified by cytosolic N-acetylations of AF and PABA (rapid, intermediate and slow). In addition, cross-mating experiments with intra- and inter-phenotype animals confirmed that hepatic AT-II isozyme is inherited by a Mendelian co-dominant trait. These results indicate that the polymorphic appearance of an acetyltransferase, AT-II, is responsible for the N-acetylation polymorphism in individual hamsters.

N-acetyltransferase 2 genetic polymorphism: effects of carcinogen and haplotype on urinary bladder cancer risk

“…The molecular basis for slow acetylator phenotype is NAT2 gene deletion in the rabbit (Blum et al, 1989), a nonsense single-nucleotide polymorphism (SNP) yielding a truncated NAT2 enzyme in the Syrian hamster (Ferguson et al, 1994(Ferguson et al, , 1996Nagata et al, 1994), and missense SNP(s) in the mouse and rat . Both NAT1 and NAT2 have been identified and partially purified from Syrian hamster liver Smith and Hanna, 1986;Trinidad et al, 1989;Ozawa et al, 1990), intestine (Smith and Hanna, 1986), colon (Hein et al, 1993a), prostate and urinary bladder cytosols. Expression of NAT1 and NAT2 isozymes also has been reported in rapid and slow acetylator mouse and rat (Hein et al, 1991a) liver cytosols.…”

DNA Adduct Levels and Intestinal Lesions in Congenic Rapid and Slow Acetylator Syrian Hamsters Administered the Food Mutagens 2‐Amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP) or 2‐Amino‐3‐methylimidazo[4,5‐f]quinoline (IQ

“…Both humans (Blum et al 1990;Grant et al 1991;Hein et al 1993b) and Syrian hamsters (Hein et al 1985;Smith & Hanna 1986;Ozawa et al 1990) express two Nacetyltransferase isozymes (NAT1 and NAT2) which differ in substrate specificity and genetic control. The N-acetylation capacity is subject to a genetic polymorphism both in humans and hamsters (Weber & Hein 1985;Hein 1988;Kadlubar et al 1992;Grant 1993).…”

Activities of Drug-Metabolizing Enzymes in the Liver of <i>Suncus murinu</i><i>s</i>: Possible Lack of N-Acetyltransferase Activity in Liver Cytosol

“…Recently, cDNA clones encoding two types of NAT were isolated from human liver cDNA libraries [16,17]. The presence of two forms of NAT has also been proven in other animal species such as rabbits and ham-203 sters [18,19], Both forms of NAT exert activi ties on many substrates, though the activities are dependent on the substrates. Thus, it may be possible that suncus possesses no NAT activities in liver cytosol.…”