Lipid composition of functional domains of the lymphocyte plasma membrane

Abstract

Plasma membrane vesicles from calf T-lymphocytes were fractionated by affinity chromatography on Con A-Sepharose. One subfraction eluted freely from the affinity column (fraction 1), while a second one adhered specifically to the column (fraction 2). While both fractions were derived exclusively from the plasma membrane, fraction 2 carried the high-affinity receptor for the mitogen concanavalin A and was distinct from fraction 1 with respect to its polypeptide pattern and the content of some plasma membrane-associated enzymes, suggesting the existence of functional plasma membrane domains. These functionally distinct fractions showed different lipid composition. The adherent fraction was enriched in phosphatidylcholine, while the relative amount of phosphatidylethanolamine and phosphatidylserine was reduced. Furthermore, the relative amount of saturated fatty acids was enhanced in the phospholipids of the adherent plasma membrane fraction. This could be shown in total phospholipids, as well as in separated individual phospholipids. We could therefore demonstrate that lipid heterogeneity may exist in plasma membranes of cells without structural polarity. Similar results were obtained when T-lymphocytes were stimulated with the mitogen concanavalin A. The functional domain, consisting of the high-affinity concanavalin A receptor, several enzymes and distinct lipid compositional pattern, thus seems to constitute a relatively stable structural entity of the lymphocyte plasma membrane.