Iodide uptake activities of NIS mutants. HepG2 cells were transfected with pcDNA3.1/lacZ and pcDNA3.1 (mock), wild-type (wt), R9A, E79A, R82A, K86A, D163A, H226A, R228A, D233A, D237A, R239A, R241A, D311A, D322A, or D331A DNAs. Twenty-four hours later, iodide uptake abilities and β-galactosidase activities were determined as described in Materials and Methods. Iodide uptake abilities are expressed as relative iodide uptake, which is present as the comparison with the radioactivity relative to wt. β-Galactosidase activities are expressed as OD420. Values are mean ± standard error of triplicate assays.