INTERACTION OF SPORANGIOMYCIN WITH THE BACTERIAL RIBOSOME

The peptide antibiotic sporangiomycin specifically inhibits protein synthesis when added to growing cultures of Bacillus subtilis. A study on the reactions for bacterial protein synthesis in cell-free systems has shown that sporangiomycin interferes with specific reactions responsible for peptide-chain elongation, while it has no effect on peptide chain initiation. The primary action of the antibiotic appears to be on the 50 S ribosomal subunit. This is suggested by the observation that ribosomes pre-treated with sporangiomycin are inactive in protein synthesis and that the inhibition can be overcome by an excess of 50 S subunits. Furthermore, 35S-labelled sporangiomycin binds specifically to 50 S particles. Step-wise release of groups of ribosomal proteins by treatment with increasing concentrations of LiCl has shown that a specific fraction (the 1.3-1.7 M LiCl split proteins) is essential for antibiotic binding to the 50 S particle. It is hypothesized that sporangiomycin inhibits protein synthesis by binding to a ribosomal multimolecular site of the utmost importance in the process of peptidechain elongation.