Fast translocation of phosphatidylcholine to the outer membrane leaflet after its synthesis at the inner membrane surface in human erythrocytes.
The translocation rate of [14C]phosphatidylcholine to the outer membrane leaflet of human erythrocytes after its primary synthesis from lysophosphatidylcholine by acylation with 14C-labeled oleic or palmitic acid in the inner leaflet has been measured by following the time-dependent increase of cleavability of 14C-labeled phospholipids by external phospholipase A2 (5 min, 37 degrees C). Immediately after a short acylation time period of 10 min about 20% of the newly synthesized [14C]phosphatidylcholine are already detectable in the outer leaflet. After an incubation of 1 h at 37 degrees C following 10 min of acylation the fractions of labeled and native phosphatidylcholine accessible to the lipase are identical, which demonstrates that [14C]phosphatidylcholine has attained the same asymmetric distribution as its endogenous analogue. The calculated halftime of the outward translocation is about 20 min and its activation energy is low, 30 kJ/mol. Translocation is inhibited by a 5 min treatment with phenylglyoxal following acylation. A fast translocation is not observed for newly synthesized phosphatidylethanolamine. Results suggest a selective, protein-mediated outward translocation of newly synthesized phosphatidylcholine.
Andrick
C
C
Institut für Physiologie, Medizinische Fakultät, RWTH Aachen, F.R.G.
Bröring
K
K
Deuticke
B
B
Haest
C W
CW
D000215:Acylation; D001692:Biological Transport; D002478:Cells, Cultured; D004910:Erythrocyte Membrane / Q000378:metabolism*; D006801:Humans; D008244:Lysophosphatidylcholines / Q000097:blood; D019301:Oleic Acid; D009829:Oleic Acids / Q000378:metabolism; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism; D010713:Phosphatidylcholines / Q000097:blood*
D008244:Lysophosphatidylcholines; D009829:Oleic Acids; D010169:Palmitic Acids; D010713:Phosphatidylcholines; D019301:Oleic Acid; D019308:Palmitic Acid