RAT-LIVER CHROMATIN PHOSPHOLIPIDS

To shed Light on the question whether the phospholipids present in chr omatin are native or are due to contamination from nuclear membranes, we labeled the phospholipids of isolated nuclei and determined the amo unt of phospholipids (PL) and PL fatty acid composition in nuclei and chromatin. The hepatocyte nuclei were isolated and radioiodinated by t he lactoperoxidase method under saturating and nonsaturating condition s, and the radioactivity associated with chromatin extracted from thes e nuclei was monitored. Whereas 97% the label was recovered in the nuc lear 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%) phosphatidylcho line (14%), and sphingomyelin (35%). In sphingomyelin of chromatin-ass ociated 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.