title: Thiol-dependent changes in the properties of rat liver sulphotransferases.
abstract: 1. Two enzymes (A and B) which catalyse the sulphation of p-nitrophenol and l-tyrosine methyl ester have been isolated from female rat livers. One of these enzymes (A) also catalyses the sulphation of dehydroepiandrosterone. 2. The K(m) values for the sulphation of p-nitrophenol and l-tyrosine methyl ester by enzyme B at pH7.5 are 1.5mum and 2.9mm respectively. 3. Enzyme B is oxidized on keeping at 0 degrees C when the K(m) and V(max.) values for the sulphation of p-nitrophenol are increased approx. 200-fold and fourfold respectively. This oxidized preparation of enzyme B fails to catalyse the sulphation of l-tyrosine methyl ester. 4. When the oxidized form of enzyme B is kept at 0 degrees C and low ionic strength then further forms of p-nitrophenol sulphotransferase are produced having even lower affinities for the sulphate acceptor. 5. The K(m) value for adenosine 3'-phosphate 5'[(35)S]-sulphatophosphate is not affected during storage of the enzyme under these conditions. 6. Prolonged storage of enzyme B at low ionic strength leads to a considerable degree of polymerization of p-nitrophenol sulphotransferase and l-tyrosine methyl ester sulphotransferase. 7. The changes in the kinetic properties and molecular size of enzyme B during storage are reversed by dithiothreitol.
mesh_terms: D000227:Adenine Nucleotides / Q000378:metabolism; D000818:Animals; D002384:Catalysis; D002845:Chromatography; D003080:Cold Temperature; D003687:Dehydroepiandrosterone; D004229:Dithiothreitol / Q000494:pharmacology; D004952:Esters / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008970:Molecular Weight; D009596:Nitrophenols / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats; D013438:Sulfhydryl Compounds; D013466:Sulfurtransferases; D014443:Tyrosine / Q000378:metabolism
chemical_list: D000227:Adenine Nucleotides; D004952:Esters; D009596:Nitrophenols; D013438:Sulfhydryl Compounds; D014443:Tyrosine; D003687:Dehydroepiandrosterone; D013466:Sulfurtransferases; D004229:Dithiothreitol