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 pl asma membranes, were used in interaction studies with the major plasma memb rane lipid components, phosphatidylcholine (PC) and phosphatidylethanolamin e (PE), With molecular species combinations, representative for plant plasm a membranes, packing conditions during compression of monolayers of PC/PE m ixtures with different amounts of PA or Cer added, were investigated, In co ntrast to the behaviour of single PA or single Cer, which exhibited condens ed compression curves, as compared with curves representative for phosphogl ycerides, the triple mixtures of PC/PE with. PA or Cer showed markedly expa nded monolayer films, These data were evaluated as a spontaneous heterogene ous dispersion of PA and Cer in the PC/PE mixture. Membrane vesicles produc ed with different amounts of PA added to a PC/PE mixture of 1:1 (mol/mol) h ad an almost linear increase in permeability for glucose (chosen as a commo n polar low-molecular mass metabolite) with increasing percentage PA. The p resence of PA in plasma membranes and its possible function are discussed i n relation to recent reports on anionic protein-lipid interactions, PC/PE v esicles with different amounts of Cer added did not influence the permeabil ity for glucose at 2.5 and 5 mol%, but did so, significantly, at 7.5 and 9 mol%.