Effect of pH on the kinetic properties of rat skeletal muscle AMP deaminase.

1. The optimal pH for activity of rat skeletal muscle AMP deaminase depends on substrate and salt concentrations. 2. At pH 7.12, differently from what is observed at acidic pH, the sigmoid kinetics shown by the enzyme in the absence of salt are not reversed to a hyperbolic one by increasing KCl concentration. 3. At alkaline pH the enzyme is also more sensitive to inhibition by nucleoside triphosphates, which enhance the sigmoidicity of the substrate saturation plot. At acidic pH, ATP elicits negative cooperativity for substrate and the same phenomenon is induced by high salt concentration. 4. The different properties of the enzyme at acidic and alkaline pH suggest that AMP deaminase can exist in either of two different conformations; at physiological pH the less active form of the enzyme predominates.