Chemical composition of the plasma membrane from epimastigote forms of Trypanosoma cruzi

The chemical composition of two plasma membrane fractions from epimastigote forms of Trypanosoma cruzi is reported. Fraction M, a preparation obtained by conventional methods of cell fractionation is composed of 31% proteins, 34% lipids, 16% carbohydrates and 3% of the lipopeptidophosphoglycan. Phospholipids and sterols account for 7.5 and 9%, respectively, of the total mass. Phosphatidylethanolamine is the major phospholipid in fraction M, representing 45% of the total membrane phospholipids. The other fraction, fraction V (vesicles), was obtained by treatment of the cell with a vesiculating agent. This fraction contains 42% lipids, 20% carbohydrates, 13% proteins and 21% of the lipopeptidophosphoglycan. Phospholipids and sterols make up 17 and 8%, respectively, of the total mass of this fraction. Phosphatidylcholine and phosphatidylethanolamine are the main phospholipids found in fraction V. Phosphonolipids and sialic acid have not been detected in either membrane fraction. Sodium dodecyl sulphate polyacrylamide gel electrophoretic analysis show that the glycoproteins ABC and the lipopeptidophosphoglycan are 50- and 10-times more concentrated, respectively, in fractions V and M than in the whole cell homogenate. The high molar sterol/phospholipid ratio found in fraction M suggests that this fraction is less fluid than fraction V, perhaps reflecting a migration of certain membrane components in the presence of the vesiculating agent. Hence, fraction M is, probably, more representative of the epimastigote plasma membrane as a whole than fraction V.