Effect of Pi on the digestion pattern of T. maritima CopA with papain. SDS–PAGE was performed as described in Experimental Procedures. Purified CopA (0.5 mg/mL) was incubated with 0.5 mg/mL papain at 50 °C for 30 min in the presence of 1 mM BCS (no copper) or 10 μM CuCl2, in the presence of various concentrations of Pi as indicated by the numbers above the gels: lane 2, 0 mM; lane 3, 0.5 mM; lane 4, 1 mM; lane 5, 2 mM; lane 6, 5 mM; lane 7, 10 mM; and lane 8, 20 mM. Lane 1 contained a nondigested control.