The effect of vitamin C on N-Acetyltransferase activity in Klebsiella pneumoniae

This study was designed to assess the effect of vitamin C on arylamine N-acetyltransferase (NAT) activity in Klebsiella pneumoniae by using HPLC to measure the acetylation of 2-aminofluorene (2-AF) with and without vitamin C. Two assay systems were performed, one with intact bacterial cell suspensions, the other with S-9 fractions (9000 g supernatant). It was found that vitamin C promoted NAT activity in K. pneumoniae in a dose-dependent manner in both systems. 4 and 8 mm vitamin C were selected for further studies in S-9 fractions and intact cell systems, respectively. Through a 4-hr time course study, vitamin C promoted the N-acetylation of 2-AF in both assay systems, but, the longer the reaction time lasted, the lower the promotion rate. In the kinetic studies, vitamin C increased the value of Km from 0.42 ± 0.03 mm to 2.43 ± 0.87 mm in S-9 fraction assays and from 0.54 ± 0.03 mm to 0.85 ± 0.18 mm in intact cell assays. Vitamin C also increased the apparent Vmax values from 3.52 ± 0.08 to 39.66 ± 9.81 nmol/min/mg protein in S-9 fraction assays, and from 1.28 ± 0.06 to 4.88 ± 0.87 nmol/min/1010 CFU in intact cell assays, for acetylation of 2-AF. In the presence of vitamin C, the NAT activity was increased from 0.58 ± 0.06 to 1.34 ± 0.02 nmol/min/mg protein in S-9 fractions, and from 0.18 ± 0.02 to 0.40 ± 0.02 nmol/min/1010 CFU in intact cells, for acetylation of 2-AF. From the present study, it is concluded that vitamin C does promote the N-acetylation of 2-AF in K. pneumoniae. This is a first report suggesting that oral vitamin C may be involved in modifying the mutagenicity/carcinogenicity of ingested arylamines through enhancing the NAT activity of human enteric bacteria. This interaction should be pursued in future in vivo studies.