Abstract
Arginase was purified about 800-fold from the supernatant of rat liver homogenate and subdivided into four isozymes by isoelectric forcusing. The values of isoelectric point of these four isozymes were estimated to be pH 9.3, 9.2, 9.0, and 8.8, respectively. Manganese ion was released from enzyme molecules during the procedure of isoelectric forcusing. After addition of Mn2+, the enzyme activities of each pI isozymes were increased about 2 times than that of original activities. The pI 9.0 isozyme was most stable for heat-inactivation at 60°C among these pI isozymes. The apparent Km value of arginase for L-arginine was calculated to be 20 mM, but the values of pI isozymes were to be 29 mM (pI 9.2 and 9.0 isozymes) and 32 mM (pI 9.3 and 8.8 isozymes) . The molecular weight of the arginase was estimated to be approximately 120, 000 by Sephadex G-100 gel filtration, but the molecular weight of pI isozymes were between 90, 000 to 95, 000. L-Ornithine (20 mM) and L-proline (20 mM) inhibited the enzymatic activities of pI isozymes, but carbamyl phosphate (20 mM) had no effect.
