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Structural and functional aspects of protein: phospholipid interactions in surfactant.

Lung surfactant lipids require the presence of a specific protein and calcium ions in order to form surface films rapidly at air-water interfaces. Film formation is a necessary first step in maintenance of low surface tensions in the lung. We have studied some of the factors involved with the lipid-protein interactions in reassembled complexes as well as in isolated lung surfactant. For both of these systems, removal of apoprotein or calcium ions results in impaired surface spreading. Increasing the amounts of this apoprotein relative to phospholipid results in increased lipid-protein association, increased vesicle aggregation, and increased monolayer film formation at the air-water interface in the surface balance.