Effects of 3'-phosphoadenosine 5'-phosphate on the activity and folding of phenol sulfotransferase

Known spectroscopic and kinetic data are used to formulate pathways of the physiological and transfer reactions and the substrate inhibition of phenol sulfotransferase. Kinetic mechanisms indicate that release of PAP from enzyme complex is required for the physiological reaction but not for the transfer reaction. The pathways explain rate difference between the physiological and transfer reactions since the release of PAP is the rate- limiting step of the former reaction. Two enzyme species of phenol sulfotransferase which distinguish the physiological and transfer reaction were found to involve the binding of PAP. Differences between two forms of phenol sulfotransferase, α and β, indicate that they assemble through different folding process. It is demonstrated that only α enzyme renatures in the presence of PAP and ,β enzyme renatures only in the absence of PAP in vitro. In the over-expressed system, formation of α and β phenol sulfotmnsferase is also dependent on the availability of PAP in Escherichia colt'. It is concluded that folding of phenol sulfotransferase is assisted by PAP to form α enzyme. In the absence of PAP, β form of phenol sulfotransferase is produced.