CHARACTERIZATION OF EXPRESSED HUMAN PHENOL-SULFATING PHENOL SULFOTRANSFERASE - EFFECT OF MUTATING CYS(70) ON ACTIVITY AND THERMOSTABILITY

The cDNA for human liver phenol-sulfating phenol sulfotransferase (P-P ST) has been cloned and the active enzyme expressed in Cos cells and b acteria. Analysis of the sequence identified two cysteine residues, on e of which is highly conserved in the phenol sulfotransferase gene fam ily. Previous studies with the pure human liver enzyme suggested that the conserved cysteine may be involved in binding substrates. Bacteria l expression of P-PST with the cysteine converted to a serine indicate s that the cysteine is not essential for activity or substrate binding , however, the mutant enzyme is significantly more sensitive to therma l inactivation.