A nucleotide sequence that had been proposed for, but not identified as, rat liver aryl sulfotransferase (EC 220.127.116.11) was prepared in an appropriate vector and transformed intoEscherichia coli. The protein, expressed in large amounts, was not aryl sulfotransferase (EC 18.104.22.168) but rather tyrosine-ester sulfotransferase (EC 22.214.171.124), a sulfotransferase also active with phenols but having a much wider substrate range that includes hydroxylamines and esters of tyrosine. The recombinant tyrosine-ester sulfotransferase was identified by its unique substrate spectrum, by comparison with three peptides that were sequenced from homogeneous tyrosine-ester sulfotransferase isolated directly from rat liver, and by the specificity of antibody raised to the rat liver enzyme. Two isoforms were obtained, each of which was difficult to solubilize upon sonication ofE. coli. Both forms were solubilized with a solution of polyols (glycerol and sucrose) and subsequently purified to homogeneity.