Incorporation of radioactive free fatty acids into glycerolipids of subcellular fractions from human tonsil lymphocytes.

Human tonsil lymphocytes were cultured with phytohemagglutinin (PHA) for 1-72 hr. Throughout the culture periods studied, PHA stimulated similarly the synthesis of triacylglycerol, phosphatidylcholine and phosphatidylethanolamine from radioactive free fatty acids. There was no significant difference in the stimulation of cellular uptake of different labeled fatty acids tested (palmitic, stearic, oleic and arachidonic acids). Human tonsil lymphocytes were shown to be composed of heterogeneous cell populations with respect to the activities of cellular uptake of free fatty acids. The cells were subfractionated after being labeled with radioactive fatty acids for 6 hr. We found that the light and heavy plasma membranes, which are known to occur in human tonsil lymphocytes, are distinctly different from each other with respect to the labeling patterns of glycerolipids and also to the response to PHA. In the light plasma membranes, the labeling of phospholipids relative to that of triacylglycerol was much less than that of heavy plasma membranes and other organelles, though radioactivity of phosphatidylcholine per mg protein of light plasma membranes was the highest of any other organelles. Furthermore, the stimulation of phosphatidylcholine synthesis by PHA appeared most markedly in the light plasma membranes in comparison to other subcellular fractions.