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. (Author)
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