Properties of plant plasma membrane lipid models - bilayer permeability and monolayer behaviour of glucosylceramide and phosphatidic acid in phospholipid mixtures

Phosphatidic acid (PA) and glucosylceramide (Cer), constituents of plant plasma membranes, were used in interaction studies with the major plasma membrane lipid components, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), With molecular species combinations, representative for plant plasma membranes, packing conditions during compression of monolayers of PC/PE mixtures with different amounts of PA or Cer added, were investigated, In contrast to the behaviour of single PA or single Cer, which exhibited condensed compression curves, as compared with curves representative for phosphoglycerides, the triple mixtures of PC/PE with. PA or Cer showed markedly expanded monolayer films, These data were evaluated as a spontaneous heterogeneous dispersion of PA and Cer in the PC/PE mixture. Membrane vesicles produced with different amounts of PA added to a PC/PE mixture of 1:1 (mol/mol) had an almost linear increase in permeability for glucose (chosen as a common polar low-molecular mass metabolite) with increasing percentage PA. The presence of PA in plasma membranes and its possible function are discussed in relation to recent reports on anionic protein-lipid interactions, PC/PE vesicles with different amounts of Cer added did not influence the permeability for glucose at 2.5 and 5 mol%, but did so, significantly, at 7.5 and 9 mol%.