A critical study of amino acid incorporation into protein by isolated liver mitochondria from adult rats.

1. Mitochondria were isolated from rat liver in a way that kept bacterial contamination at a minimum. 2. The activity of oxidative phosphorylation was unchanged under these conditions, whereas the ability of the preparations to incorporate amino acids into protein was insignificant, though it could be enhanced somewhat by the presence of EDTA. This enhancement was sensitive to ribonuclease. 3. The active time of incorporation did not exceed 15min. at 30 degrees . 4. Microsomal contamination, as measured by glucose 6-phosphatase activity, was about 5%. 5. The ability of isolated bacteria to incorporate amino acids into protein was greatly enhanced by the addition of mitochondria or heat-inactivated mitochondria. 6. A correlation was found between the growth rate of bacteria and the amino acid-incorporating activity. 7. Amino acid incorporation by combined mitochondrial-bacterial systems was inhibited by 2,4-dinitrophenol. 8. The results confirm and extend the earlier findings made in our Laboratory that isolated liver mitochondria, when free from contaminating bacteria and obtained from adult rats, are not able to catalyse the incorporation of amino acids into protein at a measurable rate. 9. The results are discussed with special emphasis on the validity of these findings.