Differential activation of promutagens by alloenzymes of human sulfotransferase 1A2 expressed in Salmonella typhimurium.

Various enzymatically formed sulfuric acid esters are chemically reactive and mutagenic. This metabolic activation pathway is not detected in standard in-vitro mutagenicity test systems. We describe the construction of Salmonella typhimurium TA1538-derived strains expressing alloenzymes *1, *2, *3, *5, 6 of human sulfotransferase 1A2 (SULT1A2). The reference compounds, 1-hydroxymethylpyrene (1-HMP), N-hydroxy-2-acetylaminofluorene (OH-AAF) and 2-hydroxylamino-5-phenylpyridine (OH-APP), were activated to mutagens in these strains. Their activity differed 7- to 16-fold between strains expressing various alloenzymes. It was strongest and weakest in the strains expressing the common alloenzymes, 1 and 2, respectively. The SULT1A2 protein expression levels, and the V(max) and K(m) values with the reference substrate 4-nitrophenol, varied 2.5-, 4-, and 110-fold, respectively, in cytosolic preparations from strains TA1538-SULT1A21 and 2. Strains with varying protein levels were constructed via insertion of silent mutations in the 5'-part of the cDNA. TA1538-SULT1A21Z and TA1538-SULT1A22Y showed equal expression levels of alloenzymes 1 and 2, respectively, which were 3 times above those of TA1538-SULT1A21. The mutagenicity of OH-AAF and OH-APP was unchanged in strain TA1538-SULT1A21Z versus 1, and moderately increased in TA1538-SULT1A22Y versus 2. The influence of the protein level was stronger with 1-HMP. Nevertheless, mutagenic activity of 1-HMP was still 11 times higher in TA1538-SULT1A21Z than in TA1538-SULT1A22Y. Thus, differences in the properties between alloenzymes can lead to differences in the activation of promutagens. The model compounds were also tested in strains expressing the other ten human SULTs identified. Whereas OH-AAF and OH-APP showed the highest mutagenic activities in strains expressing SULT1A2, 1-HMP was more potent in strains expressing other SULT forms. With the limitation that little is known about the tissue distribution and regulation of SULT1A2, the findings suggest that its polymorphism may affect the individual susceptibility towards procarcinogens, in particular certain aromatic amines and amides.