FIG 1.

IC₅₀ determination for positive controls in the A/T assay. (A and B) Titrations of spiramycin (A) and fusidic acid (B) in an A/T assay. The concentrations of spiramycin ranged from 0.02 to 10.0 μM, and the concentration of fusidic was from 4 to 256 μM. The antibiotics were diluted into DMSO, so that the concentration of DMSO was the same as in the screening assays. Positives were control assays in which there were no antibiotics, and approximately 500 pmol of phenylalanine were synthesized in these assays. The curve fits and IC₅₀s were determined using XLfit 5.3 (IDBS) as part of Microsoft Excel.