SUMMARY: Chloramphenicol (1 mg./ml.) increased the mean doubling time of from 3.6 to 5 hr and gave 62% inhibition of the final yield of organisms on an acetate + mineral salts + thiamine medium. The rates of acetate oxidation and tetrazolium reduction by whole organisms decreased progressively when grown in the presence of increasing Chloramphenicol concentrations; no ultrastructural abnormalities of the mitochondria of such organisms were seen in electron micrographs. Succinoxidase and NADH oxidase activities of isolated mitochondria were decreased by 43% and 72%, respectively, by growth of organisms with I mg. chloramphenicol/ml. The content of cytochromes (a+a) was decreased by 40%, and cytochrome oxidase activity was about 50% that of normal mitochondria. No alteration in the activities of rotenone-sensitive NADH-cytochrome oxidoreductase or succinate-cytochrome oxidoreductase was detected, using mammalian cytochrome as electron acceptor. However, the rate of reduction of electron-transport components during the aerobic-anaerobic transition (with succinate as substrate) suggested that the supply of electrons to the respiratory chain was rate-limiting and might be more important in leading to respiratory deficiency than the decreased cytochrome oxidase activity. No major cytochrome dislocation was detected, suggesting that the respiratory chain was itself intact.


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