... analysis, the purified enzymewas activated by incubation with 2 mm MnCl2in 10 mm Tris ⁄ HCl pH 8.0 for 30 min at 37 °C, and then the free metalion was removed by dialysis against 10 mm Tris ⁄ HCl ... measuring the formation of urea from l-arginine or agmatine in50 mm glycine ⁄ NaOH pH 9.0. In studying the effect ofpH on enzyme activities, buffers used were 50 mm Tris ⁄ HCl pH 7–8.7 and 50 mm glycine ... manganeseions, because metal -free species were totally inactive in the absence of added Mn2+. At the optimum pH, the Kmfor agmatine (2.5 ± 0.2 mm) was very close to the Kmof the wild-type arginase...