Detection of Cholera Toxin by Optical Methods: A Mechanism-Based Approach to the Generic Detection of Protein Toxins

Methods to monitor the ADP-ribosyltransferase activity of cholera toxin fragment A were investigated. Ultraviolet spectroscopy was a suitable technique when the acceptor molecule contained a chromophore. Toxin catalyzed ADP-ribosylation of acceptor molecules, which do not contain a chromophore but do contain an amino group, can be monitored by labeling the acceptor molecule with a fluorescent probe after its ADP-ribosylation. The sensitive technique of fluorescence spectroscopy can be employed to monitor the action of cholera toxin without regards to the substituents on the acceptor molecule by use of epsilon NAD, the fluorescent analogue of NAD.