When chloramphenicol (500 μg./ml.) is added to an exponentially growing culture of growth is completely inhibited within a few generations. Organisms from chloramphenicol-inhibited cultures have a greater number of small mitochondria; growth and division of mitochondria is apparently uncoupled from the growth and division of the organisms. Growth for 72 h. in the presence of chloramphenicol did not lead to any significant alteration in the cytochrome content per cell or per mg. of protein of isolated mitochondria. The latter show greatly decreased oxygen uptake rates with 2-oxoglutarate and with succinate as respiratory substrates, and increased sensitivity to the site I inhibitors, rotenone and piericidin A. Respiratory control was not detectable and the oligomycin sensitivity of the -ATPase is reduced in mitochondria from cells grown with the antibiotic. After inoculation into medium not containing chloramphenicol, these respiratory-deficient organisms grew normally after a lag of 24 h. Impaired coupling of oxidative phosphorylation is not seen in mitochondria from organisms starved for 24 h. in the presence of chloramphenicol. This suggests that the turnover of enzymes involved in phosphorylating electron transport proceeds only very slowly in the absence of net growth when chloramphenicol is present.


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