Action of ubenimex on aminopeptidase activities in spleen cells and peritoneal macrophages from mice.

The action of ubenimex on aminopeptidase (APase) activity was studied in intact spleen cells and peritoneal macrophages from mice. Ubenimex strongly inhibited hydrolyzing activities against arginine-beta-naphtylamide (Arg-NA), Lys-NA and Pro-NA in both cells. Inhibition of hydrolysis of Leu-NA, Met-NA and Ala-NA was relatively small or not observed. When both cells were incubated in HANKS' solution, hydrolyzing activities against Arg-NA, Lys-NA and Pro-NA were released to the medium, while Leu-NA and Met-NA-hydrolyzing activities were mostly bound. In addition, the Leu-NA-hydrolyzing activity in the spleen cells was kinetically studied. The Arg-NA and Leu-NA-hydrolyzing activities in four fractions prepared from the homogenate of spleen cells were also studied kinetically. From these studies it was suggested that ubenimex inhibits aminopeptidase B and a Pro-NA-hydrolyzing enzyme more effectively than Leu-APase in intact spleen cells and peritoneal macrophages from mice.