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Phospholipid Content of Mitochondrial and Microsomal Membranes from Morris Hepatomas of Varying Growth Rates¹

Department of Medicine, Veterans Administration Medical Center and the University of California, San Diego, California 92161 [K. Y. H., B. D. Z.], and The Department of Biochemistry, Howard University, Washington, D. C. 20001 [H. P. M.]

Mitochondria and microsomal membranes were prepared from normal, fetal, and regenerating rat liver and from seven Morris hepatomas of varying growth rates and analyzed for percentage of phospholipid composition and phospholipid content per mg protein. The Morris hepatomas studied included the 7777, 5132tc, 7800, 7794A, 7787, 9633, and 9618A.

Cardiolipin is localized in mitochondria in all tissues studied. The sphingomyelin percentage and content are increased in mitochondria of fetal rat liver and more rapidly growing hepatomas, 7777, 5123tc, and 7794A but are similar to those of normal liver in hepatomas with slower growth rates. The ratio of the percentage of phosphatidylethanolamine to that of phosphatidylcholine in mitochondria and microsomes is not substantially altered in most of the seven hepatomas and in the rapid growth controls. Our studies do not support the concept of equalization of membrane phospholipid composition in hepatomas with regard to the subcellular localization of cardiolipin and the ratios of percentage of phosphatidylethanolamine to that of phosphatidylcholine. However, our results confirm the increased percentage of sphingomyelin in the membranes of hepatomas with very rapid growth rates.

Substantial changes in the membrane phospholipid content per mg of protein are present in the seven Morris hepatomas. The mitochondrial phospholipid content per mg of protein is substantially increased in nearly all of the hepatomas and in fetal liver but appears to be normal in regenerating rat liver. Microsomal phospholipid per mg of protein is considerably decreased in nearly all of the hepatomas and in the rapid growth controls. Changes in membrane phospholipid content per mg of protein appear to be of a greater quantitative significance in these Morris hepatomas than are alterations in the percentage of phospholipid composition of the respective membrane fractions.

¹ Supported by Research Service of the San Diego Veterans Administration Medical Center.

² Recipient of USPHS Grant CA 15694.

³ Present address: Graduate Department of Biochemistry, University of California, Davis, Calif.

⁴ Recipient of USPHS Grant CA100792.

Received 12/19/78. Accepted 4/24/79.

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