Adenylate Deaminase

Abstract A procedure is described for purifying adenylate deaminase from calf brain. The method involves salt precipitation from the soluble protein of brain followed by heat treatment, diethylaminoethyl cellulose column chromatography, and either sucrose density gradient centrifugation or gel filtration. The final purification is 180-fold. The enzyme is activated by adenosine triphosphate and by alkali metal ions. The most effective alkali metal ion is that of lithium. Ammonium and tetramethylammonium ions have no effect on activity. The activators do not alter the pH optimum of the enzyme, which is about pH 6.2. ATP protects the enzyme against heat inactivation. Some kinetic properties of the enzyme in the presence and in the absence of ATP and LiCl are presented. A plot of the reaction rate with respect to the AMP concentration in the absence of activators yields a curve with a pronounced sigmoidal shape. Addition of LiCl yields similar curves which are displaced to the left. Addition of ATP yields curves which approximate rectangular hyperbolas. The effect of both activators is thus to increase the apparent affinity of the enzyme for AMP without affecting the maximum reaction velocity. Conversely, increasing the concentration of AMP has the effect of increasing the apparent affinity of the enzyme for ATP. Addition of LiCl also increases the apparent affinity of the enzyme for ATP.