title: Evidence for cooperative effects in human liver arginase.
abstract: The reaction kinetics of human liver arginase (L-arginine amidinohydrolase, EC 3.5.3.1) in terms of arginine concentration is strikingly altered by varying the pH. Lowering the pH from the optimum (9.5) toward a more physiological value (7.5) there is a transition from hyperbolic to sigmoidal kinetics. The cooperative effects are observed in the presence and absence of the product ornithine. Dimers of arginase exhibit typical Michaelis-Menten kinetics even in the presence of ornithine. Dimer-dimer interactions are suggested to explain the kinetic properties of arginase at pH 7.5.
mesh_terms: D001119:Arginase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001667:Binding, Competitive; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D046911:Macromolecular Substances; D009952:Ornithine / Q000494:pharmacology
chemical_list: D046911:Macromolecular Substances; D009952:Ornithine; D001119:Arginase