Effect of Spermine on the Binding of Erythromycin to Escherichia coli Ribosomes and the Peptidyl‐Transfer Reaction

Effect of spermine on the binding of erythromycin to ribosomes from Escherichia coli (Q13) and on N ‐acetylphenylalanyl‐puromycin (AcPhe‐puromycin) synthesis on the ribosomes was studied under various ionic conditions.1 Spermine inhibited the binding of erythromycin to ribosomes. The inhibitory effect was diminished with increasing concentration of Mg 2+ or monovalent cation such as K+ or NH 4+ . 2 The preincubation of ribosomes with spermine strongly decreased the affinity of ribosomes to erythromycin. The affinity of spermine‐treated ribosomes was restored by subsequent incubation with high concentration of NH 4+ . These inactivation and reactivation processes were strongly dependent on the incubation temperature. 3 At a high concentration of Mg 2+ (16 mM), AcPhe‐puromycin synthesis was inhibited by the addition of spermine, although the binding of N ‐acetylphenylalanyl‐tRNA (AcPhe‐tRNA) to ribosomes was not affected. 4 At a low Mg 2+ (5 mM) concentration, AcPhe‐tRNA · ribosome complex formation and AcPhe‐puromycin synthesis were stimulated by the addition of relatively low concentration of spermine. Further additions of spermine resulted in marked reductions of AcPhe‐puromycin synthesis, while AcPhe‐tRNA · ribosome complex formation was little affected. 5 The inhibition by spermine of AcPhe‐puromycin synthesis was reduced by increasing concentration of K+ or NH 4 +, regardless of the concentration of Mg 2+ . These results suggest that spermine binds to ribosomes and the incubation of the spermine · ribosome complex at physiological temperature induces an alteration of ribosome conformation and consequent changes in the ribosomal functions.