Studies on the advent of ureotelism. The effects of bivalent cations on the capacity of the hepatic arginase of the Mexican axolotl to hydrolyse endogenous arginine.

1. The effects of 19 bivalent cations on the activity, stability and capacity to hydrolyse endogenous arginine of axolotl liver arginase were studied. 2. It was found that Fe(2+), Co(2+), Ni(2+) and Zn(2+), as well as Mn(2+), stabilize the enzyme and render it able to hydrolyse endogenous arginine. 3. By using different concentrations of Co(2+) and Ni(2+) it was possible to dissociate the effect of each of the metal ions on the activity and stability of arginase from that on its capacity to hydrolyse endogenous arginine. 4. The effects of Mn(2+), Co(2+) and Ni(2+) on the activity and stability of arginase in the homogenate were also observed with purer preparations of the enzyme. 5. It is suggested that the capacity to hydrolyse endogenous arginine is a consequence of the integration of arginase with the arginine-formation sites.