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 su pply of catalyst sufficiently abundant to identify suboptimal substrat es. Such large quantities are particularly useful when working with th e enzymes of detoxication, a family of proteins that are distinguished by their broad substrate specificity for generally lipophilic compoun ds, i.e., by their very low specifcity for features other than the fun ctional group [1]. We have achieved bountiful expression of a sulfotra nsferase active with phenols [2], an enzyme originally purified and ch aracterized from rat liver [3], and classified as tyrosine-ester sulfo transferase, EC 2.8.2.9 [4,5], but usually referred to as rat liver ph enol or aryl sulfotransferase IV. Having improved the sensitivity and versatility of some of the assays for sulfotransferases, we examined t he substrate spectrum of this enzyme. As presented here, the results o f 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 exp eriments also establish a greater catalytic scope for the natural rat liver enzyme than that previously described.