Phospholipid transmethylation in the membrane of human neutrophils and lymphocytes.
Phospholipid transmethylation in the microsomal fraction of stimulated and unstimulated human leukocytes was measured in a recently developed assay system. Microsomal fraction was prepared from neutrophils, unseparated lymphocytes, T lymphocytes, and non-T lymphocytes by sonication and subsequent ultracentrifugation. Two hundred micrograms of microsomal protein was reacted with S-adenosyl-L-[methyl-3H]methionine. In unstimulated cells, incorporation of methyl-3H into phospholipid was 0.60 +/- 0.06 pmol min-1 mg protein in neutrophil membrane, 0.84 +/- 0.075 in unseparated lymphocytes, 1.23 +/- 0.17 in T lymphocytes, and 0.71 +/- 0.085 in non-T lymphocytes (mean +/- SE). Stimulation of neutrophils with opsonized zymosan or concanavalin A (Con A), and of lymphocytes with Con A, phytohemagglutinin, or pokeweed mitogen increased 15 to 30%. The resulting methylated phospholipids were identified and quantitated by two-dimensional thin-layer chromatography. The inhibitor 5'-S-isobutyl-5'-deoxyadenosine (SIBA) inhibited transmethylation 47-55%. This assay system appears to measure specifically the activity of methyltransferases which mediate the transmethylation of membrane phospholipid; the assay should find important applications in the study of membrane lipid metabolism in human health and disease.
D002855:Chromatography, Thin Layer; D003208:Concanavalin A / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D008214:Lymphocytes / Q000201:enzymology*; D008563:Membrane Lipids / Q000097:blood*; D008780:Methyltransferases / Q000037:antagonists & inhibitors / Q000097:blood*; D009504:Neutrophils / Q000201:enzymology*; D050918:Phosphatidylethanolamine N-Methyltransferase; D010743:Phospholipids / Q000097:blood*; D010835:Phytohemagglutinins / Q000494:pharmacology; D011043:Pokeweed Mitogens / Q000494:pharmacology; D013601:T-Lymphocytes / Q000201:enzymology; D014461:Ultracentrifugation; D015054:Zymosan / Q000494:pharmacology
D008563:Membrane Lipids; D010743:Phospholipids; D010835:Phytohemagglutinins; D011043:Pokeweed Mitogens; D003208:Concanavalin A; D015054:Zymosan; D008780:Methyltransferases; D050918:Phosphatidylethanolamine N-Methyltransferase