Subcellular localization, metal ion requirement and kinetic properties of arginase from the gill tissue of the bivalve Semele solida

Abstract

Arginase activity (3.1 ± 0.5 units/g (wet wt) of tissue) was found associated to the cytosolic fraction of the gill cells of the bivalve Semele solida. The enzyme, with a molecular weight of 120,000 ± 3000, was partially purified, and some of the enzymic properties were were examined. The activation of the enzyme by Mn 2+ followed hyperbolic kinetics with a K Mn value of 0.10 ± 0.02 μM. In addition to Mn 2+, the metal ion requirement of the enzyme was satisfied by Ni 2+, Cd 2+ and Co 2+; Zn 2+ was inhibitory to ail the Values of K m for arginine and K i for lysine inhibition, were the same, regardless of the metal ion used to activate the enzyme; K m values were 20 mM at pH 7.5 and 12 mM at the optimum pH of 9.5. Competitive inhibition was caused by ornithine, lysine and proline, whereas branched chain amino acids were non competitive inhibitors of the enzyme.