Transition State Structure for the Hydrolysis of NAD Catalyzed by Diphtheria Toxin.

Diphtheria toxin (DTA) uses NAD(+) as an ADP-ribose donor to catalyze the ADP-ribosylation of eukaryotic elongation factor 2. This inhibits protein biosynthesis and ultimately leads to cell death. In the absence of its physiological acceptor, DTA catalyzes the slow hydrolysis of NAD(+) to ADP-ribose and nicotinamide, a reaction that can be exploited to measure kinetic isotope effects (KIEs) of isotopically labeled NAD(+)s.