Binding of [14C]erythromycin to Escherichia coli ribosomes

Binding of erythromycin to the 50S ribosomal subunit is affected by alterations in the 30S ribosomal subunit

Expression of resistance to erythromycin in Escherichia coli, caused by an altered L4 protein in the 50S ribosomal subunit, can be masked when two additional ribosomal mutations affecting the 30S proteins S5 and S12 are introduced into the strain (Saltzman, Brown, and Apriion, 1974). Ribosomes from such strains bind erythromycin to the same extent as ribosomes from erythromycin sensitive parental strains (Apirion and Saltzman, 1974). Among mutants isolated for the reappearance of erythromycin resistance, kasugamycin resistant mutants were found. One such mutant was analysed and found to be due to undermethylation of the rRNA. The ribosomes of this strain do not bind erythromycin, thus there is a complete correlation between phenotype of cells with respect to erythromycin resistance and binding of erythromycin to ribosomes. Furthermore, by separating the ribosomal subunits we showed that 50S ribosomes bind or do not bind erythromycin according to their L4 protein; 50S with normal L4 bind and 50S with altered L4 do not bind erythromycin. However, the 30S ribosomes with altered S5 and S12 can restore binding in resistant 50S ribosomes while the 30S ribosomes in which the rRNA also became undermethylated did not allow erythromycin binding to occur. Thus, evidence for an intimate functional relationship between 30S and 50S ribosomal elements in the function of the ribosome could be demonstrated. These functional interrelationships concerns four ribosomal components, two proteins from the 30S ribosomal subunit, S5, and S12, one protein from the 50S subunit L4, and 16S rRNA.

Spectrophotometric assay for cephalosporin C in fermentation broths

Several N-substituted erythromycylamines were evaluated for their ability to inhibit the binding of [¹⁴C]erythromycin to ribosomes. The association and dissociation constants for the binding of each compound to Escherichia coli ribosomes were determined. These studies have resulted in the development of three types of probes for topological studies of the erythromycin-binding site and the ribosome: the chemically reactive bromoacetamido, the photoreactive N-(2)-nitro-4-azidophenyl)glycinamido, and the fluorescent fluorescein isothiocyanate derivatives of 9(S)-erythromycylamine.

Hedamycin, a new antitumor antibiotic. I. Production, isolation, and characterization

We examined the effect of leucomycins, leucomycin derivatives, and other 16-membered macrolides (tylosin, niddamycin, spiramycin I, and spiramycin III) on [ 14 C]erythromycin binding to ribosomes. Results of these studies enabled determination of the association and dissociation constants for the binding of each of these compounds to Escherichia coli ribosomes. In addition, the binding of the leucomycins and the leucomycin derivatives to ribosomes in general correlated with their antimicrobial activity.

Reversal by syngeneic spleen cells of inhibitory effects of drugs and irradiation on Friend virus

The dissociation constants for binding to ribosomes from Escherichia coli and concentrations at which 50% inhibition of [¹⁴C]erythromycin binding to ribosomes occurred were determined for 45 erythromycin analogues. These values were correlated with their antibacterial activities against Bacillus subtilis. Compounds which bound to ribosomes best showed the greatest activities; those which were poorly bound to ribosomes showed little or no antibacterial activity. The ribosomal binding assays therefore reflected the general antibacterial potential of the erythromycin analogues.

Effect of erythromycin analogues on binding of [14C]erythromycin to Escherichia coli ribosomes

The relative ability of 44 erythromycin analogues to bind to ribosomes was determined by their effect on [(14)C]erythromycin binding to Escherichia coli ribosomes. The association and dissociation constants of each of these erythromycin derivatives were determined as well as their interaction coefficient for their binding to ribosomes. Substitutions were made on various portions of the erythromycin molecule with retention of substantial activity as measured by inhibition of [(14)C]erythromycin binding to ribosomes. Since the effect of erythromycin analogues on [(14)C]erythromycin binding to ribosomes provides a relatively sensitive assay for these compounds, erythromycin analogues with relatively little affinity for ribosomes could be detected. Compounds with association constants of 10(4) M(-1) were detectable; the association constant for erythromycin binding to ribosomes was approximately 10(8) M(-1). Thus, compounds with 0.0001 the association constant of erythromycin were detectable. This assay could be used alone or in conjunction with microbiological assays for primary screening of active analogues or other compounds which interfere with [(14)C]erythromycin binding to ribosomes. It permits an estimate of the general activity of compounds rapidly and directly. Variables such as metabolic modifications of the compounds and permeability are excluded. The present assay reflects the ability of the compounds to interact directly with their target organelle and may serve as a useful adjunct in developing new compounds.