Protection of mammalian cells from diphtheria toxin by exogenous nucleotides

Abstract
Exogenous nucleotides were found to protect mammalian cells from the lethal effects of diphtheria toxin. Protective potency of a given nucleotide was base specific and phosphate chain length dependent. Full expression of protective potency required an intact nucleotide, but the effect did not appear to be mediated by nucleotide-induced phosphorylation. Nucleotides antagonized the binding of diphtheria toxin to its cell surface receptor in a manner that correlated with the degree of protection. It was concluded that cellular protection from diphtheria toxin by nucleotides results from inhibition of toxin–receptor binding and that nucleotides therefore may serve as valuable research tools for future studies.