title: A unique reactive residue in adenosine triphosphate phosphoribosyltransferase sensitive to five conformation and dissociation states.
abstract: Adenosine triphosphate phosphoribosyltransferase is inactivated rapidly by bulky alkylating reagents in a biphasic reaction.  The initial inactivation rate is dependent upon an optimal concentration of histidine and is more rapid at low enzyme concentrations and low ionic strength.  A histidine-free dimer form of the enzyme is the proposed reactive species.  The dimer is shown by ultraviolet difference spectroscopy to bind histidine about 1 order of magnitude more weakly than the hexameric form of the enzyme.  Alkylated enzyme is similar to native enzyme in dissociation and histidine-binding properties.  Native enzyme must exist at significant levels in at least five different conformational and dissociative states to account for the inactivation behavior.
mesh_terms: D000081:Acetamides / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000477:Alkylating Agents / Q000494:pharmacology; D002850:Chromatography, Gel; D004229:Dithiothreitol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006639:Histidine / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009154:Mutation; D009282:Naphthalenesulfonates / Q000494:pharmacology; D009596:Nitrophenols / Q000494:pharmacology; D009994:Osmolar Concentration; D010430:Pentosyltransferases / Q000037:antagonists & inhibitors*; D010754:Phosphoribosyl Pyrophosphate; D011487:Protein Conformation; D012486:Salmonella typhimurium / Q000201:enzymology
chemical_list: D000081:Acetamides; D000477:Alkylating Agents; D009282:Naphthalenesulfonates; D009596:Nitrophenols; D006639:Histidine; D010754:Phosphoribosyl Pyrophosphate; D000255:Adenosine Triphosphate; D010430:Pentosyltransferases; D004229:Dithiothreitol