Copper and silver transport by CopB-ATPase in membrane vesicles of Enterococcus hirae

The P-type ATPase, CopB, of Enterococcus hirae is required for the copper resistance displayed by this organism and thus was postulated to be a copper pump. Using 64Cu+ and 110mAg+, we here show ATP-driven copper and silver accumulation catalyzed by CopB in native inside-out membrane vesicles of E. hirae. CopB ATPase exhibited an apparent Km for Cu+ and Ag+ of 1 microM and for ATP of 10 microM. Transport was maximal at pH 6 and had an apparent Vmax of 0.07 nmol.min-1.mg-1 for both copper and silver transport. Vanadate displayed a biphasic effect on transport: maximal inhibition was observed at 40 microM vanadate for copper transport and 60 microM for silver transport, respectively. At higher vanadate concentrations, these inhibitions were reversed. The CopB ATPase of E. hirae is thus a pump for the extrusion of monovalent copper and silver ions, with copper probably being the natural substrate.