Bacterial contamination and amino acid incorporation by isolated mitochondria.

The data presented in this paper emphasize the importance of eliminating bacterial contamination in studies of amino acid incorporation into isolated mitochondria. A correlation between the number of bacteria present and amino acid incorporation into mitochondria was observed when pure cultures of bacteria were added to mitochondria prepared under sterile conditions. Low concentrations of dinitrophenol, presumably a selective inhibitor of amino acid incorporation into mitochondria, inhibited amino acid incorporation into some species of bacteria. In addition, a lack of correlation between amino acid incorporation and bacterial growth in time studies has been demonstrated. These results suggest that the criteria advanced by various workers to indicate that bacterial contamination is of little importance in studies of amino acid incorporation into mitochondria are insufficient. Mitochondrial preparations essentially free of bacterial contamination (less than 100 bacteria per ml of incubation medium) can incorporate amino acids into their protein in the presence of adenine nucleotides, Mg++, phosphate, a complete amino acid mixture, ethylenediaminetetraacetate, and succinate.