Identification and functional characterization of arylamine N-acetyltransferases in eubacteria: Evidence for highly selective acetylation of 5-aminosalicylic acid

Arylamine N-acetyltransferase activity has been described in various bacter ial species. Bacterial N-acetyltransferases, including those from bacteria of the gut flora, may be involved in the metabolism of xenobiotics, thereby exerting physiopathological effects. We characterized these enzymes furthe r by steady-state kinetics, time-dependent inhibition, and DNA hybridizatio n in 40 species, mostly from the human intestinal microflora. We report for the first time N-acetyltransferase activity in 11 species of Proteobacteri aceae from seven genera: Citrobacter amalonaticus, Citrobacter farmeri, Cit robacter freundii, Klebsiella ozaenae, Klebsiella oxytoca, Klebsiella rhino scleromatis, Morganella morganii, Serratia marcescens, Shigella flexneri, P lesiomonas shigelloides, and Vibrio cholerae. We estimated apparent kinetic parameters and found that 5-aminosalicylic acid, a compound efficient in t he treatment of inflammatory bowel diseases, was acetylated with a catalyti c efficiency 27 to 645 times higher than that for its isomer, 4-aminosalicy lic acid. In contrast, para-aminobenzoic acid, a folate precursor in bacter ia, was poorly acetylated. Of the wild-type strains studied, Pseudomonas ae ruginosa was the best acetylator in terms of both substrate spectrum and ca talytic efficiency. DNA hybridization with a Salmonella enterica serovar Ty phimurium-derived probe suggested the presence of this enzyme in eight prot eobacterial and four gram-positive species. Molecular aspects together with the kinetic data suggest distinct functional features for this class of mi crobial enzymes.