Photolabelling of cholera toxin subunits during membrane penetration

Abstract
A compound which will specifically label intramembranous sections of the toxin should label the channel-forming B subunits but not the channel-contained A1 subunit. This prediction was tested with a photoreactive glycolipid compound and the opposite result was obtained. Probably only the A1 subunit enters the membrane (Newcastle disease virus system) and data on the kinetics of that process are provided.