Abstract
Nacetyltransferase 2 (NAT2) catalyzes Nacetylation
and Oacetylation of many drugs and environmental
carcinogens. Genetic polymorphisms in the NAT2
gene have been associated with differential susceptibility
to cancers and drug toxicity from these compounds.
Single nucleotide polymorphisms (SNPs)
have been identified in the human NAT2 coding region.
A new allele, NAT2*19, possessing the C190T
(R64W) exchange, was recently identified. In order to
understand the effect of this new SNP, recombinant
NAT2*4 (reference) and NAT2*19 were expressed in
yeast (Schizosaccharomyces pombe). The C190T
(R64W) SNP in NAT2*19 caused substantial reduction
in the NAT2 protein level and stability, but did not
cause significant reduction in transformation efficiency
or mRNA level. The enzymatic activities for Nacetylation
of two arylamine carcinogens (2-aminofluorene,
4-aminobiphenyl), and a sulfonamide drug
(sulfamethazine) were over 100-fold lower for NAT2
19 compared to reference NAT2 4. Kinetic studies
showed a reduction in Vmax but no significant change
in substrate Km. In addition, the SNP caused significant
reduction in the Oacetylation of the Nhydroxy
2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine.
These results show that NAT2*19 possessing the
C190T (R64W) SNP encodes a slow acetylator phenotype
for both N and Oacetylation, due to a reduction
in the amount and stability of the NAT2 19 allozyme.
Catalytic properties and heat stabilities of novel recombinant human N-acetyltransferase 2 allozymes support existence of genetic heterogeneity within the slow acetylator phenotype
