A, representative Western blot of lysates of MDTF cells expressing PiT1-13-HA mutants containing individual cysteines L545C, Y546C, L547C, V548C, Y549C, D550C, V554C, and K557C. B, lysates of cells expressing above mutant proteins treated with MTSET prior to B-mal labeling. C, lysates of MDTF cells expressing PiT1-13-HA mutants containing individual cysteines R581C, L591C, and T592C reacted with B-mal. D, lysates of cells expressing above mutants permeabilized with SLO before B-mal labeling. PiT1-HA is the positive control for SLO.