NAD dependent inhibition of protein synthesis by Pseudomonas aeruginosa toxin

P. aeruginosa toxin (PA toxin) inhibits protein synthesis in a reticulocyte cell free system. The inhibition requires NAD and results in a block at an elongation step of polypeptide assembly. PA toxin was found to act like diphtheria toxin fragment A. Both toxins catalyze the transfer of radioactivity from nicotinamide (U ¹⁴C) adenine dinucleotide ([¹⁴C]NAD) into covalent linkage with the 100,000 dalton elongation factor 2 (EF 2) protein. Furthermore, in the presence of a limiting amount of EF 2, excess toxin, and [¹⁴C] NAD, the two toxins were non additive in the amount of label transferred to EF 2. Unlike free fragment A of diphtheria toxin, the enzymatic activity of PA toxin is heat labile and neutralizable with antibody to PA toxin but not with antibody to fragment A. Although PA and diphtheria toxins have different cellular specificities and molecular properties and produce different clinical symptoms, their intracellular mechanisms of action appear to be identical.