Mechanism of posttranslational regulation of phenol sulfotransferase: expression of two enzyme forms through redox modification and nucleotide binding.

Sulfotransferase catalyzes sulfuryl group transfer between a nucleotide and a variety of nucleophiles that may be sugar, protein, xenobiotics, and other small molecules. Nucleotides may serve as cosubstrate, cofactor, inhibitor, or regulator in an enzyme catalyzed sulfuryl group transfer reaction. We are trying to understand how nucleotide regulates the activity of phenol sulfotransferase (PST) through the expression of two enzyme forms. The homogeneous rat recombinant PST was obtained from Escherichia coli, and the nucleotide copurified was examined. The nucleotide was completely removed from inactive PST in high salt and oxidative condition. Total enzyme activity was recovered following incubation in reductive environment. Many nucleotides are known to tightly bind to PST but only one nucleotide, 3'-phosphoadenosine 5'-phosphate (PAP), was identified to combine with PST by ion-pair RP-HPLC, UV-visible spectra, (31)P NMR, and ESI-MS and MS-MS spectrometry. In addition to the presence or absence of PAP, oxidation following reduction of PST was required to completely interconvert the two forms of PST. According to the experimental results, a mechanism for the formation of the two enzyme forms was proposed.