Effect of spermine on the binding of erythromycin to Escherichia coli ribosomes and the peptidyl-transfer reaction.

Abstract

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 Mg2+ or monovalent cation such as K+ or NH4+. 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 NH4+. These inactivation and reactivation processes were strongly dependent on the incubation temperature. 3 At a high concentration of Mg2+ (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 Mg2+ (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 NH4+, regardless of the concentration of Mg2+. 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.