Abstract
1. 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. 2.|Up to 10 μM, 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. 3.|AMP deaminase is inactivated by incubation with the periodate oxidation product of ATP. The (oxidized ATP)—AMP deaminase complex stabilized by NaBH 4 reduction shows kinetic properties similar to those of the native enzyme in the presence of high ATP concentrations. 4. 4.|A plausible explanation of the observed cooperativety is that ATP induces different conformation states of AMP deaminase subunits, causing the substrate to follow a sequential mechanism of binding to enzyme. 5. 5.|Binding of the radioactive oxidized ATP shows that 3.2 mol of this reagent bind per mol AMP deaminase.
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