Lysines in the KKSKK have a redundant function. WT or Lys 16, Lys 17, Lys 19, Lys 20 α1-A549 cells were exposed to 1.5 % O2 for 60 min. At the end of the incubation, Na,K-ATPase endocytosis was studied as described above. Top, quantitative densitometric scan of three experiments (mean ± SEM), **p<0.01, bottom representative Western blot of the α1-subunit abundance.