STUDIES ON THE MODE OF ACTION OF DIPHTHERIA TOXIN

Using tritium-labelled toxin, it was shown that HeLa cells treated with a saturating dose take up less than 2 0.005ugml of the added toxin within a 5-hour period. Diphtheria toxin exerts its action on cells by inhibition of protein synthesis. Low concentrations of toxin block the incorporation of C14-amino acids into protein in extracts of HeLa cells and of rabbit reticulo cytes. It was shown that the toxin interferes with a step involving the transfer of aminoacids from aminoacyl-sRNA to the growing polypeptide chain. A method for phage assay has been developed using an anti- head protein serum gammaglobulin fraction, trace labelled with I131. Bacteria to which 4 or more phage particles have been absorbed are specifically agglutinated by the serum. As determined by the I131 method, the classic PW8 strain releases less than 2 as much absorbable phage following UV induction as do Pbeta d under similar conditions.