Entrance of cholera enterotoxin subunits into cells.

Quantitative analysis of the staining of cholera enterotoxin on the surface of cells with specific antibodies against each subunit of cholera toxin, using a Fluorescence-Activated Cell Sorter, showed that not only subunit A but also subunit B penetrates the cell membrane. The detection of each subunit inside the cell was facilitated by the use of saponin, an agent which increases membrane permeability.