Abstract
1. 1. Arginase activity was detected in homogenates prepared from the gill of the sea mollusc Concholepas concholepas. From this tissue a partially purified preparation (sp. act. 30 units/mg of protein) was obtained and characterized. 2. 2. The metal ion requirement of the enzyme is satisfied by Mn 2+, Co 2+ and Ni 2+ and a significant inhibition of the Mn 2+-activated enzyme is caused by Cd 2+, Mg 2+ and Zn 2+. 3. 3. The enzyme exhibits Michaelis-Menten kinetics and at the pH optimum of 9.5 the K m for arginine was found to be 25 mM. Lysine and the product ornithine are competitive inhibitors while the inhibition caused by branched chain amino acids and proline is non-competitive. 4. 4. The enzyme has a molecular weight of about 27,500, which is in the order of the molecular weight of the subunits of oligomeric arginases. The molecular weight of the enzyme from Concholepas concholepas is not altered by addition or withdrawal of metal ions.
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