Inhibitory Effect of Spermine on Ribosomal Peptidyltransferase

A cell-free system derived from Escherichia coli has been used to study the kinetics of inhibition of peptide bond formation by spermine at optimal Mg2+ concentration (10 mM). With the aid of the puromycin reaction, it was possible to show that spermine does not affect the final degree of peptide bond formation. However, sperm-me inhibits peptide bond formation at the kinetic phase of the reaction. A single molecule of spermine participates in the mechanism of inhibition. The type of inhibition of peptide bond formation by spermine is simple competitive, regardless of whether the ternary complex AePhetRNA-poly(U)-ribosome (complex C) is formed in the presence (Ki = 190 μM) or in the absence (Ki = 84 μM) of factors washable from ribosomes. Preincubation experiments of spermine with the individual components of complex C demonstrated that the inhibitory effect of spermine is closely related with its binding to AcPhetRNA.