RAT-LIVER CHROMATIN PHOSPHOLIPIDS

To shed Light on the question whether the phospholipids present in chromatin are native or are due to contamination from nuclear membranes, we labeled the phospholipids of isolated nuclei and determined the amount of phospholipids (PL) and PL fatty acid composition in nuclei and chromatin. The hepatocyte nuclei were isolated and radioiodinated by the lactoperoxidase method under saturating and nonsaturating conditions, and the radioactivity associated with chromatin extracted from these nuclei was monitored. Whereas 97% the label was recovered in the nuclear membranes, only 0.08-0.6% was found in chromatin. The PL present in chromatin were relative to the amounts present in the entire nuclei and calculated as percentage of total, phosphatidylethanolamine (10%), phosphatidylserine (22%), phosphatidylinositol (19%) phosphatidylcholine (14%), and sphingomyelin (35%). In sphingomyelin of chromatin-associated PL an enrichment in polyunsaturated fatty acids was seen. The data indicated that the PL found in isolated chromatin do not seem to be due to contamination from the nuclear membrane.