Pseudomonas aeruginosa exoenzyme S: an adenosine diphosphate ribosyltransferase distinct from toxin A.

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Abstract
P. aeruginosa exoenzyme S is an ADP ribosyltransferase distinct from Pseudomonas toxin A. Exoenzyme S catalyzes the transfer of radioactivity from all portions of radiolabeled NAD+ except nicotinamide. Digestion of the radiolabeled product(s) formed in the presence of [adenine-14C]NAD+ and exoenzyme S with snake venom phosphodiesterase yields only AMP, suggesting that ADP-ribose is present as monomers and not as poly(ADP-ribose). Exoenzyme S does not catalyze the transfer of ADP-ribose from NAD+ to elongation factor 2, as do toxin A and diphtheria toxin, but to 1 or more other proteins present in crude extracts of wheat germ or rabbit reticulocytes and in partially purified preparations of elongation factor 1. The ADP-ribosyltransferase activity of exoenzyme S is distinct from toxin A by several tests: it is not neutralized by toxin A antibody, it is destroyed rather than potentiated by pretreatment with urea and it is more heat stable. These latter observations and the substrate specificity suggest that exoenzyme S is different from any previously described prokaryotic ADP-ribosyltransferase.