Amino acylaminonucleoside inhibitors of protein synthesis: II. Effect on oligophenylalanine formation

Abstract

1. 1. The inhibition of the poly U-directed incorporation of phenylalanyl residues from l-phenylalanyl-tRNA into peptide chains by a number of antibiotics was studied in a ribosomal system from Escherichia coli. The inhibitors were amicetin, blasticidin S, chloramphenicol, gougerotin and sparsomycin. The products of incorporation were examined by column chromatography on benzoylated diethylaminoethyl cellulose. The fractions obtained were: phenylalanylphenylalanine ( Phe) 2 oligophenylalanine ( oligo Phe) and polyphenylalanine ( poly Phe). The incorporation was carried out at 10 mM Mg 2+ in the presence of various amounts of transfer factors. The rate of incorporation of phenylalanyl residues into peptide linkage as well as the distribution of peptide chain lengths varied with the concentration of these factors. 2. 2. In the presence of amicetin, blasticidin S, gougerotin or chloramphenicol, oligopeptides ( Phe) 2 and oligo( Phe) accumulated and constituted the major product of phenylalanine incorporation. Despite initial interference with ( Phe) 2, oligo Phe and poly Phe formation, the total number of peptide bonds (( Phe) 2, oligo Phe and poly Phe formed after 8 min in the presence of these inhibitors was equal to, or exceeded the number of peptide bonds obtained in their absence. At the same time, the amount of poly Phe formed in the presence of the inhibitors was consistently lower than in the control. The total phenylalanine incorporation into peptide bonds in the absence of inhibitors proceeded linearly for the entire time period examined (32 min). Oligopeptides were also accumulated in the presence of sparsomycin but total peptide bond formation was always less than in the control. Tetracycline did not cause the accumulation of oligopeptides. 3. 3. The results obtained with amicetin, blasticidin S, gougerotin or chloramphenicol cannot be explained solely on the basis of a constant interference with peptide bond formation by these antibiotics. Alternative explanations are considered.