Studies on the biosynthesis of protein and lipid components of rat liver mitochondria.

1. Male rats were injected intraperitoneally with l-[(35)S]methionine, [(32)P]-phosphate and [2-(14)C]acetate. The animals were killed at various times up to 72hr. after injection, and liver mitochondria were prepared and fractionated into soluble protein, insoluble protein and lipid for assay of the radioactivity of each fraction. 2. The maximal specific radioactivity of total mitochondrial phospholipid with respect to both (32)P and (14)C was attained after approx. 6hr. 3. (32)P was incorporated most rapidly into phosphatidylethanolamine, maximal incorporation being attained after approx. 6hr.; maximal incorporation into lecithin occurred after 6-12hr. The specific radioactivity of cardiolipin was still slowly increasing at the end of the experiment (72hr.). 4. There were no major differences between the rates of incorporation of (14)C into the lecithin, phosphatidylethanolamine and cardiolipin fractions of mitochondrial phospholipid, maximal incorporation in each case occurring after approx. 6hr. 5. Maximal incorporation of (35)S into both soluble and insoluble protein fractions was attained less than 12hr. after injection, the maximal specific radioactivity of soluble protein being higher than that of insoluble protein.