3Department of Genetics,

doi:10.1016/j.jmb.2006.06.029Introduction Humans possess two arylamine N-acetyltrans-ferases (NAT1 and NAT2), which catalyze the acetylation of arylamines, hydrazines and N-hydro-xylated metabolites through the transfer of an acetyl group from acetyl-CoA.1–3 The medical importance of the N-acetylation capabilities of NAT was first realized by its inactivation of the antitubercular drug isoniazid.4 Although human NAT1 catalyzes the acetylation of the folic acid catabolite, p-aminoben-zoylglutamic acid, no endogenous substrate has been identified for NAT2.5,6 Both of the human NAT enzymes have attracted attention because of their roles in either activating or detoxifying arylamines*Corresponding authorAbbreviations used: NAT, N-acety circular dichroism; DMSO, dimethy HA-epitope, epitope from hemagglu heteronuclear single quantum coher p-aminobenzoic acid; PNPA, p-nitro wt, wild-type. E-mail address of the correspond