title: Lipid mixing is mediated by the hydrophobic surfactant protein SP-B but not by SP-C.
abstract: Pulmonary surfactant contains two families of hydrophobic proteins, SP-B and SP-C. Both proteins are thought to promote the formation of the phospholipid monolayer at the air/fluid interface of the lung. The excimer/monomer ratio of pyrene-labeled PC fluorescence intensities was used to investigate the capacity of the hydrophobic surfactant proteins, SP-B and SP-C, to induce lipid mixing between protein-containing small unilamellar vesicles and pyrene-PC-labeled small unilamellar vesicles. At 37 degrees C SP-B induced lipid mixing between protein-containing vesicles and pyrene-PC-labeled vesicles. In the presence of negatively charged phospholipids (PG or PI) the SP-B-induced lipid mixing was enhanced, and dependent on the presence of (divalent) cations. The extent of lipid mixing was maximal at a protein concentration of 0.2 mol%. SP-C was not capable of inducing lipid mixing at 37 degrees C not even at protein concentrations of 1 mol%. The SP-B-induced lipid mixing may occur during the Ca(2+)-dependent transformation of lamellar bodies into tubular myelin and the subsequent formation of the phospholipid monolayer.
authors.affiliation: Laboratory of Veterinary Biochemistry, Utrecht University, Netherlands.
authors.forename: M A
authors.initials: MA
authors.lastname: Oosterlaken-Dijksterhuis
authors.forename: M
authors.initials: M
authors.lastname: van Eijk
authors.forename: L M
authors.initials: LM
authors.lastname: van Golde
authors.forename: H P
authors.initials: HP
authors.lastname: Haagsman
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000378:metabolism; D000818:Animals; D002413:Cations, Divalent; D006851:Hydrochloric Acid / Q000494:pharmacology; D008081:Liposomes; D008168:Lung / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D010715:Phosphatidylglycerols / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D011510:Proteolipids / Q000302:isolation & purification / Q000378:metabolism*; D011663:Pulmonary Surfactants / Q000302:isolation & purification / Q000378:metabolism*; D011721:Pyrenes; D012965:Sodium Chloride / Q000494:pharmacology; D013329:Structure-Activity Relationship; D013552:Swine
chemical_list: D002413:Cations, Divalent; D008081:Liposomes; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D010716:Phosphatidylinositols; D010743:Phospholipids; D011510:Proteolipids; D011663:Pulmonary Surfactants; D011721:Pyrenes; D015060:1,2-Dipalmitoylphosphatidylcholine; D012965:Sodium Chloride; C030984:pyrene; D006851:Hydrochloric Acid