Abstract
The puromycin reactivity of fMet-tRNA Met f ( Escherichia coli) bound to rat liver free ribosomes can be used as an assay for peptidyl transferase. Anisomycin and sparsomycin were both found to inhibit this reaction. The kinetics of the inhibition in both cases conformed to a competitive type. Sparsomycin was found to be almost a 100-fold more effective inhibitor of this reaction than anisomycin. Hydrolysis of fMet-tRNA Met f ( E. coli) by rat liver free ribosomes can be used as another index of peptidyl transferase activity. Anisomycin stimulated this reaction approximately 5-fold. Sparsomycin was shown to inhibit the anisomycin-stimulated hydrolysis of fMet-tRNA by rat liver ribosomes. The kinetics of the inhibition conformed to a “mixed” type of competitive reaction between sparsomycin and anisomycin. The fMet ethyl ester formation from fMet-tRNA Met f bound to rat liver ribosomes in the presence of ethanol was also studied. Sparsomycin and anisomycin strongly inhibited this reaction. Peptidyl transferase function, as measured in rat liver membrane-bound ribosomes prepared with deoxycholate, was similar to that in rat liver free ribosomes. This was in spite of a markedly reduced formation of the functional fMet-tRNA Met f—ribosome intermediate. Peptidyl transferase function, measured in rabbit reticulocyte ribosomes was similar to that of rat liver ribosomes.
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