title: Interaction between the erythromycin and chloramphenicol binding sites on the Escherichica coli ribosome.
abstract: The effects of chloramphenical on the binding kinetics of a fluorescein isothiocyanate derivative of 9(S)-erythromycylamine with 70S and 50S ribosomes have been studied by direct fluorimetric measurements. While chloramphenicol had little effect on the second-order 70S binding rate of the erythromycin analogue, it substantially reduced the dissociation rate of the fluorescent antibiotic-70S ribosome complex. This could be explained by simultaneous binding of both antibiotics to the 70S ribosome. The kinetic results suggest that chloramphenicol-saturated 70S particles bind the erythromycin analogue four times stronger and this was confirmed by direct binding studies. In additon, chloramphenicol causes a twofold increase in the intrinsic fluorescence of the 70S-bound analogue. This increase in fluorescence was used to study the kinetics of chloramphenicol binding to 70S  ribosomes containing the fluorescent derivative. The fluorescence change followed first-order kinetics, suggesting that chloramphenicol induces a conformational change in the 70S particle. This could explain both its effect on erythromycin binding and on the fluorescence of bound analogue. Less detailed results with the 50S particle indicate a qualitively similar picture of erythromycin-chloramphenicol interactions.
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive; D002701:Chloramphenicol / Q000378:metabolism / Q000494:pharmacology*; D004917:Erythromycin / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism / Q000648:ultrastructure*; D007700:Kinetics; D008954:Models, Biological; D012270:Ribosomes / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D000900:Anti-Bacterial Agents; D004917:Erythromycin; D002701:Chloramphenicol