PNGase F treatment of glycosylation-deficient mutant Shaker K_V channels. (A) Normalized and superimposed ionic current traces from WT Shaker K_V channels before and after PNGase F treatment, shown for comparative purposes. (B and C) Normalized and superimposed ionic current recordings before and after PNGase F treatment of oocytes expressing glycosylation-deficient N259D–N263D Shaker K_V channels (B, n = 3) and N259Q–N263Q Shaker K_V channels (C, n = 3). These experiments were performed with the same batch of PNGase F enzyme. These ionic currents were elicited in response to a voltage step to +60 mV from a holding potential of −80 mV and were recorded by using the cut-open oocyte voltage-clamp technique. DeGly, deglycosylation.