Characterization of a P-type Copper-Stimulated ATPase from Mouse Liver

Mouse liver microsomes treated with octylthioglucoside (OTG-microsomes) were examined for copper-stimulated ATPase activity. The activity was about 1 μmol Pi/mg protein/hr under optimal conditions 300 mm KCl, 3 mm MgSO₄, 10 mm GSH, 0.5 μm CuSO₄, 3 mm ATP and 50 mm acetate buffer at pH5.0]. A reducing agent such as GSH or dithiothreitol was required for the activity, and removal of Cu⁺ from the reaction mixture by bathocuporinedisulfonate resulted in a complete loss of copper-stimulated ATPase activity. Vanadate inhibited the copper-stimulated ATPase activity. The OTG-microsomes were phosphorylated in a hydroxylamine-sensitive and copper-stimulated way. Iron used instead of copper also stimulated both ATPase and phosphorylation. These results suggest that microsomes from mouse liver contain copper/iron-stimulated P-type ATPase. Received: 2 September 1998/Revised: 16 March 1999