title: Aspartate transcarbamylase of Escherichia coli. Mechanisms of inhibition and activation by dicarboxylic acids and other anions.
abstract: The interactions of several dicarboxylic acids and monoanions with Escherichia coli aspartate transcarbamylase and with its catalytic subunit have been studied by ultraviolet difference spectroscopy and steady state kinetics, with the following major findings. 1. A variety of dicarboxylic acids compete with carbamyl-P for the active sites of unliganded catalytic subunit, with steric requirements very different from those important for competition with L-aspartate for the subunit/carbamyl-P complex. Competition with carbamyl-P is much reduced if the dicarboxylic acid has a positively charged amino group. Acetate and chloride also compete. 2. At pH 7, equal concentrations of lysine acetate and L-aspartate are equally effective in displacing the transition state analog N-(phosphonacetyl)-L-aspartate (PALA) from the active sites of the concentrations of L-aspartate and lysine acetate is constant, increasing the concentration of L-aspartate does not relieve inhibition of the enzyme by PALA (Collins, K.C., and Stark, G. R. (1971) J. Biol. Chem. 246, 6599-6605). Therefore, the L-aspartate/subunit complex, like the acetate/subunit complex, must be incapable of participating in the catalytic reaction. We conclude that the kinetic mechanism is ordered, in agreement with the recent findings of Wedler and Gasser (Wedler, F.C., and Gasser, F.J. (1974), Arch. Biochem. Biophys. 163, 57-68) and in disagreement with the interpretation of Heyde et al. (Heyde, E., Nagabhushanam, A., And Morrison, J.F. (1973) Biochemistry 12, 4718-4726)...
mesh_terms: D000085:Acetates; D001221:Aspartate Carbamoyltransferase / Q000378:metabolism*; D001224:Aspartic Acid / Q000494:pharmacology; D001965:Bromides; D003998:Dicarboxylic Acids / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology*; D005650:Fumarates / Q000494:pharmacology; D007700:Kinetics; D008024:Ligands; D008298:Maleates / Q000494:pharmacology; D011189:Potassium Chloride; D011485:Protein Binding; D013386:Succinates / Q000494:pharmacology; D013644:Tartrates / Q000494:pharmacology
chemical_list: D000085:Acetates; D001965:Bromides; D003998:Dicarboxylic Acids; D005650:Fumarates; D008024:Ligands; D008298:Maleates; D013386:Succinates; D013644:Tartrates; D001224:Aspartic Acid; D011189:Potassium Chloride; D001221:Aspartate Carbamoyltransferase