Mouse Macrophage Arginase

Abstract

Mouse peritoneal macrophages in culture released a macromolecular factor capable of inhibiting mouse L1210 lymphoma cells in vitro. The factor was proved to be arginase by several criteria. The inhibition was reversed by adding arginine or citrulline to culture, the arginine in the culture medium was consumed and the guanido group of arginine was hydrolyzed exclusively to urea as demonstrated by electrophoresis and chromatography. The factor has a MW of 110,000 and a Km value of 1.0 .times. 10-2 M. These and other parameters, such as a requirement for Mn2+, alkaline pH optimum, substrate specificities and inhibition by ornithine, were similar to those of liver arginases. The arginine in the medium was decomposed by 1st-order kinetics, and the arginase activity in the supernatant of 10 .times. 106 peritoneal exudate cells/ml was enough to deplete arginine in the medium to below the level required for L1210 cells to grow in culture. Arginase activity was also detected in the peritoneal washing fluid 4 days after thioglycollate medium stimulation, suggesting in vivo enzyme release.