Photosynthetic membranes of higher plant chloroplasts are composed primarily of polar, but uncharged, galactolipids unlike most mammalian membranes which contain large amounts of phosphatidylcholine. It is unclear what role(s) the galactolipids play in maintaining the differentiated thylakoid membranes, or in stabilizing the photosynthetically active enzyme complexes. Some of the membrane complexes show no lipid selectivity for maintaining structural or functional integrity. Others are poisoned or dissociated in the presence of high concentrations of a trace lipid class. The efficiency of energy transfer and the reconstitution of protein complexes into liposomes are dependent on the lipid class employed. The lipids are asymmetrically arranged along and across the thylakoid membranes but not as distinctly as the proteins.