Lipid composition of plasma membranes from human leukemic lymphocytes

The specific activity of adenosine 5‘-monophosphatase and the concentrations of cholesterol, glucosylceramide, lactosylceramide, and phospholipids were compared in the whole homogenates and in plasma membrane fractions in four preparations of human leukemic lymphocytes taken over a 1-yr period from a patient with chronic lymphocytic leukemia. There was a 69.5-fold enrichment of the specific activity of adenosine 5’”nophosphatase in plasma membrane fractions. This enzyme appeared to be the best plasma membrane marker of all compounds studied. The increase in lactosylceramide concentration in the plasma membranes was 34.4-fold. It was significantly higher than that of glucosylceramide. The. enrichment of glucosylceramide in the plasma membranes was similar to that of cholesterol and total phospholipids. The pattern of individual phospholipids in the plasma membrane fraction, as compared with the whole homogenate, was characterized by a decrease in phosphatidylcholine and an increase in sphingomyelin. Supplementary key words adenosine 5’-monophosphatase . glucosylceramide . lactosylceramide . phospholipids Changes in lipids, especially glycolipids, have been observed during the malignant transformation in several experimental systems (1, 2). Some main characteristics of neoplastic cells such as new antigenic properties or loss of contact inhibition due to modifications in cell surface may be related to these changes (3, 4) because it is assumed that glycolipids are localized primarily if not exclusively in plasma membranes. This assumption, however, is based on studies performed in only a few tissues (5-8). In a large number of cell types this hypothesis still awaits further investigations. A method for isolation of plasma membranes from human leukemic lymphocytes was recently described by this laboratory (9), and the presence of neutral glycolipids in these cells has been previously demonstrated (1 0). The purpose of this study is to compare the distribution of glycolipids and adenosine 5’-monophosphatase (5’-AMPase), a plasma membrane marker, in the whole homogenate and in plasma membranes of human leukemic lymphocytes and to report the lipid composition of these