title: Negative homotropic cooperativity in rat muscle AMP deaminase. A kinetic study on the inhibition of the enzyme by ATP.
abstract: 1. Rat skeletal muscle AMP deaminase (AMP aminohydrolase, EC 3.5.4.6) at optimal KCl concentrations shows a biphasic response to increasing levels of the allosteric inhibitor ATP. 2. Up to 10 micrometer, ATP appears to convert the enzyme to a form exhibiting sigmoidal kinetics while at higher concentrations its inhibitory effect is manifested by an alteration of AMP binding to AMP deaminase indicative of negative homotropic cooperativity at about 50% saturation. 3. AMP deaminase is inactivated by incubation with the periodate oxidation product of ATP. The (oxidized ATP)--AMP deaminase complex stabilized by NaBH4 reduction shows kinetic properties similar to those of the native enzyme in the presence of high ATP concentrations. 4. A plausible explanation of the observed cooperativity is that ATP induces different conformational state of AMP deaminase subunits, causing the substrate to follow a sequential mechanism of binding to enzyme. 5. Binding of the radioactive oxidized ATP shows that 3.2 mol of this reagent bind per mol AMP deaminase.
mesh_terms: D000659:AMP Deaminase / Q000037:antagonists & inhibitors*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D046911:Macromolecular Substances; D009132:Muscles / Q000201:enzymology*; D009709:Nucleotide Deaminases / Q000037:antagonists & inhibitors*; D010084:Oxidation-Reduction; D011189:Potassium Chloride / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats
chemical_list: D046911:Macromolecular Substances; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D009709:Nucleotide Deaminases; D000659:AMP Deaminase