Arginase Isozymes of Rat Mammary Gland, Liver, and Other Tissues

Arginase activity accumulates in rat mammary gland during lactation, although an effective urea cycle is absent. This arginase has been partially purified and its properties have been compared to those of the purified rat liver enzyme. Conditions that allow solubilization of liver arginase leave more than 60% of the mammary gland enzyme particulate. Since solubilization requires treatment with 1-butanol, the enzyme is probably located in the membrane. Liver arginase is stable at 60°, whereas mammary gland enzyme is labile at 55°. Liver arginase has maximal catalytic activity between pH 10.0 and 10.6. At pH 10.6 the mammary gland enzyme has lost 75% of its activity. Chromatography on Sephadex G-150 separates the mammary gland activity into two fractions of different molecular weights (42,000 and 94,000), both less than that of the liver enzyme (120,000). A rabbit anti-serum that quantitatively precipitates adult and fetal liver arginases does not cross-react with the enzyme of mammary gland extracts. Arginase preparations from small intestine, kidney, and a transplanted renal carcinoma share some of these properties, and also do not cross-react with the anti-serum to liver arginase. An intermediate type of arginase found in hepatoma 7777 reacts with the antiserum, but less strongly than does liver arginase.