Incorporation of fatty acids into phosphatidylcholine is reduced during storage of human erythrocytes: evidence for distinct lysophosphatidylcholine acyltransferases.

Abstract

The incorporation of [1-14C]palmitic or [1-14C]oleic acid into phosphatidylcholine and the effect on blood group antigen expression were examined in human erythrocytes stored at 4 degrees C for 0-3 weeks. Blood drawn into EDTA was obtained by venepuncture from healthy volunteers. A 50% suspension of washed erythrocytes was incubated in buffer containing [1-14C]fatty acid for up to 60 min at 37 degrees C with moderate shaking. Phosphatidylcholine was extracted and analyzed for uptake of radiolabelled fatty acid and phospholipid phosphorus content. Incorporation of [1-14C]palmitic or [1-14C]oleic acid into phosphatidylcholine was reduced during storage. The mechanism for the reduction in radiolabelled fatty acid incorporation into phosphatidylcholine was a 64% (p < 0.05) reduction in membrane phospholipase A2 activity. Although human erythrocyte membranes isolated from freshly drawn blood are capable of reacylating lysophosphatidylcholine to phosphatidylcholine, with storage, a markedly different substrate preference between palmitoyl-Coenzyme A and oleoyl-Coenzyme A was observed. Lysophosphatidylcholine acyltransferase activity assayed with oleoyl-Coenzyme A was unaltered with storage. In contrast, lysophosphatidylcholine acyltransferase activity assayed with palmitoyl-Coenzyme A was elevated 5.5-fold (p < 0.05). Despite these changes, storage of erythrocytes for up to 3 weeks did not result in altered expression of the various blood group antigens investigated. We conclude that the incorporation of palmitate and oleate into phosphatidylcholine is dramatically reduced during storage of human erythrocytes. The observed differential in vitro substrate utilization suggests that distinct acyltransferases are involved in the acylation of lysophosphatidylcholine to phosphatidylcholine in human erythrocytes.