The predominant form of rat liver arginase, A1, and that of kidney, A4, were isolated and partially purified. 2. It was found that arginase A4, similarly as A1, has oligomeric structure. Either of the enzymes on EDTA treatment dissociates into inactive subunits of molecular weight 30 000 daltons. Addition of Mn2+ ions restores the activity and causes reassociation of subunits to the native form of 120 000 mol. wt. 3. The subunits of A4 differ considerably in electrophoretic mobility from subunits of A4, which probably is the reason why the native forms of the enzyme from kidney and liver differ in electrophoretic behaviour.
