Purple membrane and purple membrane-phospholipid Langmuir-Blodgett films

Langmuir-Blodgett films containing purple membrane fragments, which consist of the integral membrane protein bacteriorhodopsin in its native bilayer, were studied in order to determine the optimal conditions for the construction of an artificial biological membrane containing purple membrane. In pure purple membrane films, the fragments were found to aggregate at surface pressures above 15 dyn cm^-1 and desorb above 35 dyn cm^-1. At 46 dyn cm^-1 the area per bacteriorhodopsin molecule in the film equals the molecular area in a purple membrane fragment. When a synthetic phospholipid was added, to form a membrane fragment-lipid monolayer film, aggregation ceased to occur at a lipid/protein mole ratio of around 100. Desorption was still observed. The phospholipid and membrane fragment were found to be miscible and the mixing was ideal within experimental error.