Incorporation of 32P-labelled intermediates into the phospholipids of cell-free preparations of rat brain.

In previous papers (McMurray, Strickland, Berry & Rossiter, 1957b; McMurray, Berry & Rossiter, 1957a) two systems capable of supporting the incorporation of inorganic 32p into the phospholipids of rat-brain dispersions were described: (a) an anaerobic system (best demonstrated in hypotonic dispersions), which supported the labelling of lipid P under optimum conditions for glycolysis (McMurray etal. 1957 b), and (b) an aerobic system (best shown in mitochondria isolated from isotonic dispersions), which supported the labelling of lipid P under optimum conditions for oxidative phosphorylation (McMurray et al. 1957 a). The effects of metabolia inhibitors such as 2:4-dinitrophenol (DNP) and fluoride on the specific radioactivity and concentration of adenosine triphosphate (ATP) in each of these two systems suggested thlat the labelling of phospholipid was dependent upon both the prior labelling ofATP and the maintenance of adequate concentrations of this substance (McMurray et al. 1957 a). In order to elucidate some of the intermediate reactions concerned with the labelling of phospholipid from inorganic 82p, a study was made of the incorporation of82P-labelledadenosinetriphosphate (AT22P), phosphorylcholine (32PCh) and a-glycerophosphate (a-G82P) into the lipid P of the two phosphorylating systems. The distribution of radioactivity in the hydrolysis products of individual phospholipids, separated by the chromatographic method of Dawson (1954b), suggested that 82PCh and oc-G82P were incorporated into lecithin and phosphatidic acid respectively. Inorganic 32P appeared to be incorporated chiefly into phosphatidic acid and diphosphoinositide. A preliminary account of some of this work has appeared (McMurray, Berry & Strickland, 1956).