90 



NATURE, FORMATION, AND ACTIVITIES 



The most dramatic effects of chloi-amphen- 

 icol have been reported on protein syn- 

 thesis and in both bacterial and mammalian 

 tissues. Earlier work (Hahn and Wisseman, 

 1951; Saz and Marmur, 1953) had shown 

 that the antibiotic inhibited the synthesis of 

 inchiced enzymes mediating the oxidation of 

 lactose and the phosphorylation of gluconic 

 acid in E. coli. No effect of the antibiotic 

 was observed in cells previously adapted to 

 lactose and gluconate oxidation. Gale and 

 Folkes (1953) and Wisseman et al. (1954) 

 found that chloramphenicol, at growth- 

 inhibitory concentrations, specifically and 

 immediately inhibited protein synthesis in 

 bacterial cells, whereas formation of ribo- 

 nucleic acid (RNA), deoxyribonucleic acid 

 (DXA), and polysaccharide was inhibited, 

 if at all, only at much higher levels of the 

 antibiotic. 



Since these original ol)servations were 

 made, numerous confirmatory reports have 

 followed. There seems little doubt that, upon 

 addition to bacterial cultures, chlorampheni- 



col abruptly inhibits protein synthesis and 

 that presumably this inhibition accounts for 

 its antibiotic activity. Hopkins (1959), for 

 example, demonstrated that chloramphenicol 

 inhibits the incorporation of amino acids into 

 protein of calf thymus nuclei but has no 

 effect on the uptake of leucine by nuclear 

 RXA (Fig. 5). It must be noted, however, 

 that the precise locus of chloramphenicol in- 

 hibition of protein synthesis remains to be 

 delineated. 



According to Brock (1901), chlorampheni- 

 col antagonizes the action of antibiotics 

 which act on growing cells, such as penicillin 

 and streptomycin; however, it exerts an ad- 

 ditive effect upon antibiotics which also in- 

 hibit protein synthesis, such as the tetra- 

 cyclines and erythromycin. Chloramphenicol 

 inhibits the incorporation of radioactive 

 amino acids into protein. It does not inhibit 

 the activation of amino acids or transfer of 

 amino acids to soluble RXA, but it prevents 

 some step in their transfer from soluble RNA 

 to protein. A similar behavior of the tetra- 



1500 



1000 



500 



250 



/^ 



RNA(0067M choromphenicol) 



>, 



Protein (0067M choramphenicol) 



Time (minutes) 



Figure 5. Effect of chloramphenicol upon the uptake of leucine-1-C'^ (5.3 ^c per /xmole) into ribo- 

 nucleic acid and protein of calf 1h>nius nuclei. (Reproduced from Hojjkins, J. W. Proc. Natl. Acad. 

 Sci.U.8. 45:1461-1470,1959.) 



