passages.id: split_5_test_1756_passage
passages.type: progene_text
passages.text: Selective permeabilization of cells with digitonin ( to permeabilize the plasma membrane ) or Triton X-100 ( to permeabilize both intracellular and plasma membranes ) followed by immunofluorescence microscopy revealed that the carboxyl terminus of the 21 - kDa subunit is exposed on the cytoplasmic side of the membrane whereas the carboxyl terminus of the 16 - kDa subunit is located on the lumenal side of the membrane .