Cholera toxin: interaction of subunits with ganglioside GM1.

Vibrio cholerae exotoxin is an aggregate of two different noninterconvertible subunits (molecular weights about 15,000 and about 25,000). Only the smaller subunit reacts with ganglioside G(M1), a possible biological receptor. The larger subunit, found only in active toxin molecules, can be eluted with 8 molar urea from insoluble complexes of toxin, ganglioside, and cerebroside.