Hsieh S E, Lo H H, Yen Y S, Chung J G
Department of Medical Technology, Chungtai Junior College, Taichung, Taiwan, ROC.
Food Chem Toxicol. 1997 Dec;35(12):1151-7. doi: 10.1016/s0278-6915(97)85467-1.
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 (9000g 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 3.5 +/-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/10(10) 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/10(10) 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.
本研究旨在通过使用高效液相色谱法（HPLC）测量有无维生素C时2-氨基芴（2-AF）的乙酰化反应，来评估维生素C对肺炎克雷伯菌中芳胺N-乙酰基转移酶（NAT）活性的影响。进行了两个检测系统，一个使用完整的细菌细胞悬液，另一个使用S-9组分（9000g上清液）。结果发现，在两个系统中，维生素C均以剂量依赖的方式促进肺炎克雷伯菌中的NAT活性。分别选择4 mM和8 mM的维生素C用于在S-9组分和完整细胞系统中进行进一步研究。通过4小时的时间进程研究，维生素C在两个检测系统中均促进了2-AF的N-乙酰化反应，但是，反应持续时间越长，促进率越低。在动力学研究中，在S-9组分检测中，维生素C使Km值从0.42±0.03 mM增加到2.43±0.87 mM，在完整细胞检测中从0.54±0.03 mM增加到0.85±0.18 mM。对于2-AF的乙酰化反应，维生素C还使S-9组分检测中的表观Vmax值从3.5±0.08增加到39.66±9.81 nmol/min/mg蛋白质，在完整细胞检测中从1.28±0.06增加到4.88±0.87 nmol/min/10¹⁰CFU。在维生素C存在下，对于2-AF的乙酰化反应，S-9组分中的NAT活性从0.58±0.06增加到1.34±0.02 nmol/min/mg蛋白质，完整细胞中的NAT活性从0.18±0.02增加到0.40±0.02 nmol/min/10¹⁰CFU。从本研究得出结论，维生素C确实促进了肺炎克雷伯菌中2-AF的N-乙酰化反应。这是首次报道表明口服维生素C可能通过增强人肠道细菌的NAT活性参与改变摄入的芳胺的致突变性/致癌性。这种相互作用应在未来的体内研究中进一步探讨。
