title: Protective effect of elongation factor 2 on the inactivation of ribosomes by the toxic lectins abrin and ricin.
abstract: The inactivation of rabbit reticulocyte ribosomes by abrin and ricin A-chains was studied by incubating ribosomes with the A-chains and testing, after various periods of time, aliquots of the ribosomes for their ability to polymerize phenylalanine. The presence of elongation factor 2 (EF-2) reduced the rate of inactivation of ribosomes by the A-chains. The protective effect of EF-2 was strongly enhanced by GTP and, to a lesser extent, also by GDP or dGTP. Other nucleotides had no demonstrable effect. Much less protection was found after binding of Phe-tRNA to ribosomes in the presence of EF-1 (enzymic binding) or in the presence of high Mg2+ concentration (non-enzymic binding). The data indicate that when EF-2 binds to the ribosomes it completely or partially covers the target site for abrin and ricin A-chains. The possibility that EF-1 also binds to this site is discussed.
mesh_terms: D000036:Abrin / Q000494:pharmacology*; D000818:Animals; D006150:Guanine Nucleotides / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007700:Kinetics; D046911:Macromolecular Substances; D010441:Peptide Chain Elongation, Translational; D010445:Peptide Elongation Factors; D010940:Plant Proteins / Q000494:pharmacology*; D012343:RNA, Transfer / Q000378:metabolism; D011817:Rabbits; D012156:Reticulocytes / Q000187:drug effects / Q000378:metabolism; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism*; D012276:Ricin / Q000494:pharmacology*; D046249:Transfer RNA Aminoacylation / Q000187:drug effects
chemical_list: D006150:Guanine Nucleotides; D046911:Macromolecular Substances; D010445:Peptide Elongation Factors; D010940:Plant Proteins; D000036:Abrin; D006160:Guanosine Triphosphate; D012276:Ricin; D012343:RNA, Transfer