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'-monophosphatase 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.
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