Changes in substrate specificity of the recombinant form of phenol sulfotransferase IV (tyrosine-ester sulfotransferase)

The over-expression of mammalian enzymes in bacterial systems by means of recombinant DNA technology has provided the enzymologist with a supply of catalyst sufficiently abundant to identify suboptimal substrates. Such large quantities are particularly useful when working with the enzymes of detoxication, a family of proteins that are distinguished by their broad substrate specificity for generally lipophilic compounds, i.e., by their very low specificity for features other than the functional group [1]. We have achieved bountiful expression of a sulfotransferase active with phenols [2], an enzyme originally purified and characterized from rat liver [3], and classified as tyrosine-ester sulfotransferase, EC 2.8.2.9 [4,5], but usually referred to as rat liver phenol or aryl sulfotransferase IV. Having improved the sensitivity and versatility of some of the assays for sulfotransferases, we examined the substrate spectrum of this enzyme. As presented here, the results of this examination point to the limitations of enzyme nomenclature and to the danger of equating enzymes isolated from their normal habitat with those formed by recombinant technology in a foreign cell. Our experiments also establish a greater catalytic scope for the natural rat liver enzyme than that previously described.