Biochimica et Biophysica Acta, 644 (1981) 341-350 Elsevier/North-HollandBiomedicalPress BBA 79254 CHEMICAL COMPOSITION OF THE PLASMA MEMBRANE FROM EPIMASTIGOTE FORMS OF TR YPANOSOMA CR UZI JOSE FRANCO DA SILVEIRA * and WALTERCOLLI ** Departamento de Bioqufmica, Instituto de Qufmica, Universidade de S~o Paulo, C.P. 20780, S~o Paulo (Brasil) (Received November 24th, 1980) (Revised manuscript receivedFebruary 18th, 1981) 341 Key words: Membrane composition; Phospholipid; Sterol; Glycoprotein; (Trypanosoma cruz0 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 phospho- lipid 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 glyco- proteins ABC and the lipopeptidophosphoglycan are 50- and 10-times more concentrated, respectively, in frac- tions 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 com- ponents 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. Introduction Trypanosoma cruzi, the causative agent of Chagas' disease, is an unicellular organism whose life cycle involves a series of intimate interactions with the host structures.' Cell penetration, signal recognition for differentiation, and evasion from immune mechanisms, represent only a few of the phenomena vital for the maintenance of this biological cycle. As in other cell systems, these phenomena may be reasonably presumed to be dependent on plasma membrane madiation. Thus, examination of the properties of the plasma membrane from this proto- * From Instituto Butantan. ** To whom correspondenceshould be addressed. zoan may contribute to a better understanding of the mechanisms which ultimately lead to infec- tion (cf. Ref. 1). Two methods for isolation of plasma membrane from T. cruzi have recently been developed in our laboratory [2,3]. In the first method, cells are rup- tured by sonication under controlled conditions, yielding a fraction enriched in plasma membrane fragments upon differential and equilibrium density centrifugation [2]. In the other method, membrane vesicles have been obtained from epimastigote cell upon incubation with acetate pH 4.0, a condition which induces membrane vesiculation in T. cruzi [3]. The purity of both preparations has been checked by ultrastructural, biochemical and immuno- logical methods [2,3]. 0 005-2736/81/0000-0000/$02.50 © Elsevier/North-HoUand BiomedicalPress