title: Yeast argininosuccinate synthetase. Purification; structural and kinetic properties.
abstract: Yeast argininosuccinate synthetase has been purified to homogeneity. The enzyme was found to have a molecular weight of 228,000 as determined by gel sieving. It is composed of identical subunits of Mr 49,000 as shown by gel electrophoresis. The quaternary structure as determined by cross-linking of the subunits with glutaraldehyde, followed by gel electrophoresis with dodecylsulfate, is tetrameric. The saturation functions by citrulline and aspartate are hyperbolic; with MgATP as the variable substrate a sigmoid character, dependent on the concentration of citrulline, aspartate, argininosuccinate and arginine, was observed. The positive cooperativity is reduced by increasing  concentrations of citrulline and aspartate; it is increased by argininosuccinate and arginine. Kinetic analysis provided evidence for a random addition of substrates. Initial velocity studies as well as product and dead-end inhibition studies comply with a rapid-equilibrium random model, except for the interconversion of the central quaternary complexes; the different kinetic constants  have been established on the basis. Yeast argininosuccinate synthetase has a double metabolic function: anabolic in the biosynthesis of arginine, catabolic as the first enzyme of citrulline utilization as nitrogen source. The kinetic properties of the enzyme point to a physiologically well-adjusted activity for both roles and to an economic and efficient utilization of ATP.
mesh_terms: D001124:Argininosuccinate Synthase / Q000037:antagonists & inhibitors / Q000302:isolation & purification*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008025:Ligases / Q000302:isolation & purification*; D046911:Macromolecular Substances; D008970:Molecular Weight; D011487:Protein Conformation; D011489:Protein Denaturation; D012441:Saccharomyces cerevisiae / Q000201:enzymology*
chemical_list: D046911:Macromolecular Substances; D008025:Ligases; D001124:Argininosuccinate Synthase