The in vitro incorporation of 32P-labeled orthophosphate into the phosphatides of isolated rat liver mitochondria

1. 1. The incorporation of 32P i into the lipides of intact rat liver mitochondria occurs mainly into phosphatides which resemble but are not identical to phosphatidic acids and which constitute only a very small fraction of the total lipide P. Evidence is presented which indicates that one of these highly labeled phosphatides is an α,β-conjugated ester of glycerophosphate. The incorporation into the common phosphatides such as lecithin and phosphatidyl ethanolamine is extremely small in these systems. 2. 2. Glycerol, Mg, and several nucleotides such as ATP and CTP were found to stimulate the incorporation into at least 3 phosphatides one of which contains glycerophosphate. The microsomal-rich supernatant fluid also had a stimulating effect. On the other hand, cyanide, dinitrophenol, malonate, and a variety of metal ions and surface agents were found to inhibit the system. 3. 3. The identification of the mitochondrial lipides was made by chemical, infrared spectral, and paper and column chromatographic analysis. 4. 4. In contrast to intact mitochondria, the acetone powders of these particles were far less effective in incorporating 32P i into the phosphatides. However, a striking difference was found inasmuch as in these latter systems the incorporation occurred predominantly in lecithin and phosphatidyl ethanolamine and none occured in the fast moving glycerophosphatide. 5. 5. A discussion is given of the experimental findings.