Enzymatic characterization and interspecies difference of phenol sulfotransferases, ST1A forms

Cytosolic sulfotransferases, which mediate activation and detoxification of both endogenous and exogenous compounds, consist of at least five different gene families (ST1 to ST5) in mammals. Several cDNAs corresponding to ST1A forms have been reported, but their functional properties are not well characterized. In addition, only a single form of ST1A sulfotransferase has been reported in each experimental animal species despite the expressions of plural forms in humans. Therefore, enzymatic properties of human ST1A3, ST1A5, rat ST1A1, mouse St1a4, and newly isolated rabbit ST1A8 have been characterized and compared by use of their recombinant proteins to clarify the functional difference between human and experimental animal ST1A forms. From the results using more than 25 phenolic chemicals, all the experimental animal ST1A forms showed substrate specificities similar to human ST1A3 rather than ST1A5. They showed high affinities toward p-nitrophenol and 6-hydroxymelatonin as found in human ST1A3. These forms also showed high activities toward umbelliferone and naringenin, but very low activities toward catecholamines, representative substrates of human ST1A5. Hepatic contents of experimental animal ST1A forms varied (66-250 pmol/mg of cytosolic protein) but showed the same order as observed with human ST1A3 (120 pmol/mg). Hepatic content of human ST1A5 was about 19-fold less than that of ST1A3. Therefore, ST1A forms identified in experimental animal species correspond to human ST1A3 functionally. For chemicals such as troglitazone and 2-amino-4'-hydroxy-1-methyl-6-phenylimidazo[4,5-b]pyridine, clear species differences were detected among the ST1A forms examined.