The ADP-ribosyltransferase activity of the A1. subunit of cholera toxin is specifically inhibited by the dye cibacron blue 3GA. The presence of a ‘dinucleotide fold’ in the A1 subunit is thus established for the first time. This specific inhibition observed in vitro is successfully exploited in vivo for the inhibition of the diarrheal response brought out by the pure toxin in the rabbit ileal-loop test.

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