Nucleotide binding to elongation factor 2 inactivated by diphtheria toxin.

Binding of guanosine nucleotides to purified native and ADP-ribosylated wheat germ EF-2 was measured. Both forms of EF-2 bound [3H]GDP to the same extent. [3H]GDP binding to native but not to ADP-ribosylated EF-2 was reduced in the presence of GTP and ribosomes. Binding of [gamma-32P]GTP to EF-2 was significantly reduced upon ADP-ribosylation. ADP-ribosylation almost abolished both the stimulatory effect of ribosomes on GTP binding to EF-2 and the ability of EF-2 to form a high-affinity complex with GuoPP(CH2)P and ribosomes. Low-affinity complex formation between EF-2 X GDP and ribosomes was not influenced by ADP-ribosylation. The results indicate that the inhibition of the elongation process caused by the toxin is probably due to the inability of modified EF-2 to exchange GDP with GTP.