Kinetic studies of asparagine synthetase from rat liver: role of Mg2+ in enzyme catalysis.
The kinetic mechanism of asparagine synthetase from rat liver has been studied. The mechanism of the reaction in the presence of high concentrations of total Mg2+ (50 mM) was suggested to be a uni-uni-bi-ter ping-pong-type without abortive complexes; glutamine binds first followed by glutamate release, and aspartate and ATP bind in order followed by ordered release of PPi, AMP, and asparagine. But, it is indicated that in the presence of 0.5-2.0 mM excess Mg2+ over ATP the binding of substrates after the release of glutamate is in a rapid equilibrium system such as ordered Mg2+ and random aspartate-MgATP. Mg2+ was demonstrated to have two roles in the catalysis; to modify the enzyme and to form a complex of MgATP.
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D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001217:Aspartate-Ammonia Ligase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D066298:In Vitro Techniques; D007700:Kinetics; D008025:Ligases / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008274:Magnesium / Q000494:pharmacology*; D008956:Models, Chemical; D051381:Rats; D013379:Substrate Specificity
D000255:Adenosine Triphosphate; D008025:Ligases; D001217:Aspartate-Ammonia Ligase; D008274:Magnesium