Temperature-sensitivity of the weak bonds by which chloramphenicol is held in intact cells

Abstract

The temperature sensitivity of chloramphenicol bound stereospecifically by intact Escherichia coli cells was measured over the range from 0–50°. The rate of release and the total amount of releasable chloramphenicol increases with temperature. The releasable portion of the bound chloramphenicol is exchangeable with chloramphenicol in solution, but the rate of release and exchange is not affected by the concentration of the external chloramphenicol. 2 activation energies appear to be involved in release of bound chloramphenicol. From 0–25°, the activation energy is 18 000 cal/mole, while from 25–45°, the activation energy is 9000 cal/mole. The stereospecifically bound chloramphenicol is shown to be equal to 1 molecule per ribosome at saturation, and the degree of inhibition of protein synthesis by the intact cells is shown to be related to the degree of saturation of the stereospecific chloramphenicol binding sites. It is proposed that chloramphenicol is bound to a specific site on the 50-S ribosomal subunit by a 2-point sequential attachment.