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The Deacylation and Reacylation of Phosphoglyceride in Microsomes of Morris Hepatoma 7777 and Host Rat Liver¹

Department of Biochemistry, The Bowman Gray School of Medicine, Winston-Salem, North Carolina 27103 [M. W., B. P., R. M., C. C.], and Biochemical Cancer Research Unit, Howard University, Washington, D. C. 20001 [H. P. M.]

We describe here a decrease in the ratio of phospholipids to protein in microsomes prepared from Morris hepatoma 7777, compared with those from host rat liver. These microsomes, characterized by their marker enzyme content, were found to have comparable enrichment of the NADPH cytochrome c reductase. In addition to the decrease in phospholipid content, the major phospholipids had decreased polyunsaturated and increased monounsaturated fatty acids. Analysis of the free fatty acid pool of the two indicates a marked decrease in linoleic acid in this hepatoma microsome; very little longer-chain polyunsaturated fatty acid was found. The major difference in the ratio of the phospholipids was an increase in the hepatoma microsome sphingomyelin content. The hepatoma 7777 microsomes incorporated oleoyl-coenzyme A into monoacylphospholipids more rapidly than did the liver. When free fatty acids were used with an acyl-coenzyme A-generating system, the liver microsomes were more active than those from hepatoma. Furthermore, frozen and thawed microsomes from the hepatoma 7777 had little capacity to use free fatty acids, whereas liver microsomes were unaffected by freezing and thawing. These results indicate that the fatty acid-activating enzyme of hepatoma microsomes is more labile than that of liver. Both samples had phospholipase(s) that were active on the microsomal membrane phospholipids. No accumulation of monoacylphosphoglyceride was found in the hepatoma, whereas about one-half of the diacylphospholipid degraded by liver microsomes remained as the monoacylphosphoglyceride. This indicates that the precursor for reacylation in the Lands' cycle (deacylation-reacylation) is decreased in the hepatoma. We conclude from these results that, in part, the changes found in the activities of the Lands' cycle system account for the alterations in hepatoma phospholipid composition, both quantitatively and qualitatively.

¹ Supported by USPHS Grants CA 14318 and CA 10729, and by the Forsyth Cancer Service.

² Recipient of NIH Career Development Award AM 17392.

Received 1/14/77. Accepted 4/11/77.