抄録
1. Valine at a concentration of as low as 0.1μg per ml inhibited growth of strain W3110-215 (λ-F-thy-deoC-), a derivative of Escherichia coli K12, after shift-down from nutrient broth to minimal medium.
2. The inhibition by valine at this low concentration was overcome by 0.05 μg or more of isoleucine per ml.
3. On agar medium, valine-inhibition was reversed with unique recovery patterns by alanine, homoserine, leucine, methionine and threonine, suggesting the differences in their mechanisms of action.
4. Cells acquired resistance to 0.1μg of valine per ml on incubation for more than 40min in minimal medium containing threonine. The growth of these cells was still sensitive to 1.0μg or more of valine per ml. Cells incubated in the medium without threonine remained sensitive to 0.1μg of valine per ml throughout the incubation period of 6h.
5. The cells acquired resistance because threonine enhanced derepression of synthesis of acetohydroxy acid synthase, which is sensitive to valine, and maintained the repressed condition of the valine-transport system of the cells.
