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 differenc e between the physiological and transfer reactions since the release o f PAP is the rate-limiting step of the former reaction. Two enzyme spe cies of phenol sulfotransferase which distinguish the physiological an d transfer reaction were found to involve the binding of PAP. Differen ces between two forms of phenol sulfotransferase, alpha and beta, indi cate that they assemble through different folding process. It is demon strated that only alpha enzyme renatures in the presence of PAP and be ta enzyme renatures only ir. the absence of PAP in vitro. In the over- expressed system, formation of alpha and beta phenol sulfotransferase is also dependent on the availability of PAP in Escherichia coli. It i s concluded that folding of phenol sulfotransferase is assisted by PAP to form alpha enzyme. In the absence of PAT, beta form of phenol sulf otransferase is produced. (C) 1998 Elsevier Science Ireland Ltd. All r ights reserved.