Lysine in P1 or P2 disrupts ΔK_2PØ channel function but not surface expression. Wild-type (WT), S104K, or T216K ΔK_2PØ channels were studied by expression in Xenopus oocytes. (A) Sample recordings by two-electrode voltage clamp. The bath solution contained 100 mM KCl (see Materials and methods). Topology insets: blue circles denote S104K in P1 or T216K in P2. Protocol inset: holding voltage of −77 mV with 250-ms steps of 15 mV from −135 to 60 mV followed by a 100-ms step to −135 mV every 2 s. (B) Western blot analyses of channels bearing C-terminal 1D4 tags detected with anti-1D4 antibodies. Channel protein was detected among total soluble protein (left) or surface proteins isolated by biotinylation and purification with streptavidin beads (right) after SDS-PAGE (see Materials and methods). Control samples were obtained from naive oocytes. Note that monomer subunits show an anomalous apparent mass of 62 (predicted mass of 37 kD) and 56 kD after deglycosylation with peptide–N-glycosidase F (not depicted); two linked subunits migrate at 97 and 89 kD after peptide–N-glycosidase F (not depicted).