Studies on the formation of transfer ribonucleic acid-ribosome complexes. 3. The formation of peptide bonds by ribosomes in the absence of supernatant enzymes.

Peptide bond formation from aminoacyl transfer RNA and ammonium chloride-washed ribosomes can occur extensively in the absence of supernatant enzymes. More than 50% of the W-phenylalanine-tRNA can be converted into oligophenylalaninetRNA. Although diphenylalanine is the major product, the oligophenylalanine formed consisted of 73, 16, and 9.7% of di-, tri-, and tetraphenylalanine, respectively. Oligophenylalanine synthesis in the absence of supernatant factors (peptide bond synthesis) and amino acid polymerization into long polypeptides in the presence of supernatant (protein synthesis) differ in magnesium and temperature optima and other characteristics. Guanosine triphosphate is not required for the former as it is for the latter; the sulfhydryl inhibitor p-chloromercuribenzenesulfonate has little effect on the former while completely abolishing the latter. In addition, an absolute requirement for ammonium or potassium ions was shown for peptide bond synthesis itself. The results suggest that peptide bond synthesis from aminoacyl-tRNA is a property of ribosomes and is not mediated by supernatant protein factors.