Formation of 2-Amino-3-methylimidazo[4,5-f]quinoline- and 2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline-sulfamates by cDNA-expressed Mammalian Phenol Sulfotransferases

In rat liver cytosol systems, 2-amino-3-methylimidazo[4,5-f]quinoIine (IQ) and 2-amino-3,8-dimethyl-imidazo[4,5-f]quinoxaline (MelQx) were converted into their sulfamates in the presence of 3′-phosphoadenosine 5′-phosphosulfate at rates of 51.2 and 50.7 pmol/min/mg cytosol in the male, and 23.7 and 22.5 pmol/min/mg cytosol in the female, respectively. IQ-sulfamate formation was low (0.24 pmol/min/mg cytosol) in human liver cytosols, and MeIQx-sulfamate was not detected (<0.1 pmol/ min/mg cytosol). These results suggest only a minor contribution of IQ- and MeIQx-sulfamate formation to the detoxification of both heterocyclic amines in humans. Using sulfotransferase cDNA-expression systems, a rat ST1A1 arylsulfotransferase has been shown to catalyze the formation of the sulfamates, suggesting a role of the ST1A type of sulfotransferase in the N-sulfation of heterocyclic amines.