In the preferred embodiments of the detoxification mechanism the detoxifying enzyme unmasks a nucleophile which is positioned such that it will react intramolecularly with the aziridinium cation to form a 5 membered ring and concomitantly open the aziridium ring as shown below: ##STR1## The nucleophile (Nu) may be any group such as a hydroxy, thiol, amine, or carboxylate moiety.