The PQ-Loop Containing type-2 (PQLC2) protein is a lysosomal cationic amino acid transporter required for cysteamine therapy of cystinosis. Indeed, cysteamine induces formation of a mixed cysteine/cysteamine disulfide (MD) resembling lysine, which is exported from cystinotic lysosomes by PQLC2 (Jézégou et al., PNAS 2012; Liu et al., Science 2012). We previously showed that PQLC2 mediated efflux of MD is a rate-limiting step in lysosomal cystine clearance in human cystinotic fibroblasts treated with cysteamine (unpublished data, see point 2.). Here, we studied the functional properties of PQLC2 using two-electrode voltage clamp of Xenopus oocytes expressing PQLC2 at their surface. Taken together, our results sugest that both modulation of the electrical potential of the lysosomal membrane and increasing cytosolic Arg levels might accelerate efflux of the mixed disulfide from cystinotic lysosomes, thus improving cysteamine therapy.