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 (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.
Hsieh
S E
SE
Department of Medical Technology, Chungtai Junior College, Taichung, Taiwan, ROC.
Lo
H H
HH
Yen
Y S
YS
Chung
J G
JG
D015073:2-Acetylaminofluorene / Q000378:metabolism*; D001191:Arylamine N-Acetyltransferase / Q000187:drug effects / Q000378:metabolism*; D001205:Ascorbic Acid / Q000494:pharmacology*; D002273:Carcinogens / Q000378:metabolism*; D002458:Cell Fractionation; D002851:Chromatography, High Pressure Liquid; D003967:Diarrhea / Q000382:microbiology; D004305:Dose-Response Relationship, Drug; D005243:Feces / Q000382:microbiology; D006801:Humans; D007700:Kinetics; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000201:enzymology* / Q000302:isolation & purification
D002273:Carcinogens; D015073:2-Acetylaminofluorene; D001191:Arylamine N-Acetyltransferase; D001205:Ascorbic Acid