Potassium-dependent thermal sensibility of AMP-deaminase from rabbit skeletal muscle

1. AMP-deaminase (AMP-aminohydrolase, EC 3.5.4.6) from rabbit skeletal muscle showed sigmoid-shaped plots of velocity versus substrate concentration at four temperatures tested between 15 degrees and 35 degrees C. In the presence of 20 mM-KCl, the plot was sigmoid only at 30 degrees C and became hyperbolic at the other temperatures tested. In the presence of 150 mM-KCl the plots were hyperbolic at all the temperatures applied. 2. The Km value depended on temperature and concentration of KCl, whereas Vmax was the same for the 20 mM- and 150 mM-KCl-activated enzyme. 3. The value of enthalpy of the enzyme-substrate complex formation was the same for both the 20 mM- and 150-mM-KCl-activated enzyme at lower temperature range (less than 38 degrees C), whereas at higher temperatures (greater than 38 degrees C) this value was much more negative in the presence of 20 mM-KCl than of 150 mM-KCl.