title: Inhibitors of protein synthesis V. Irreversible interaction of antibiotics with an initiation complex.
abstract: The initiation complex (t-complex) formed in a cell-free system (E. coli) from Ac-Phe-tRNA, poly(U) and washed ribosomes in the presence of initiation factors (ribosomal wash) and GTP, contains the Ac-Phe-tRNA bound quantitatively in a puromycin-reactive state. The t-complex is irreversibly inactivated by spiramycin with respect to its reactivity toward puromycin. The inactivated t-complex retains all of the Ac-Phe-tRNA bound, but it does not react with puromycin (2 x10-minus-3M) within 32 min at 25 degrees. In the case of another inhibitor protein synthesis, sparsomycin, the permanently "modified" t-complex not only retains all the bound Ac-Phe-tRNA but it can still react with puromycin. In the continuous presence of sparsomycin (1 x 10-minus-7M) the bound Ac-Phe-tRNA reacts quantitatively at a rate which is one-tenth the rate at which the t-complex reacts with puromycin, at low (6.25 x 10-minus-5M) or high (2 x 10-minus-3M) concentrations. These results are not in agreement with current views according to which aparsomycin binds to the ribosome reversibly at a single site with a KI in the range of 10-minus6-10-minus-7 M and according to which this stie is at the A'-site (puromycin site) of peptidyl transferase.
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000096:biosynthesis*; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D007933:Leucomycins / Q000494:pharmacology*; D010448:Peptide Initiation Factors; D010649:Phenylalanine / Q000031:analogs & derivatives / Q000378:metabolism; D011691:Puromycin / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism; D012270:Ribosomes / Q000187:drug effects / Q000378:metabolism; D013033:Sparsomycin / Q000494:pharmacology*; D014462:Ultrafiltration
chemical_list: D000903:Antibiotics, Antineoplastic; D001426:Bacterial Proteins; D007933:Leucomycins; D010448:Peptide Initiation Factors; D010649:Phenylalanine; D011691:Puromycin; D013033:Sparsomycin; D012343:RNA, Transfer