Calcium ions and interactions of pulmonary surfactant proteins SP-B and SP-C with phospholipids in spread monolayers at the air/water interface.
Spread monolayers containing hydrophobic pulmonary surfactant protein, SP-B or SP-C, or SP-B/SP-C (2:1, w/w), alone or mixed with dipalmitoylphosphatidylcholine (DPPC) or dipalmitoylphosphatidylglycerol (DPPG), were formed on saline subphases containing calcium ions. Surface pressure-area characteristics of the films of the proteins were not affected by the presence of Ca2+ in the subphase. Calcium ions did not alter the surface properties of the binary and ternary films of DPPC plus either SP-B, or SP-C, or SP-B/SP-C (2:1, w/w). Surface pressure-area isotherms for the spread films of DPPG plus hydrophobic surfactant protein were Ca(2+)-dependent. The exclusion pressures of SP-B, SP-C and SP-B/SP-C (2:1, w/w) from protein-DPPG films in the presence of calcium were lower than the exclusion pressures in the absence of Ca2+. The divalent cation appeared to suppress the ability of SP-C and SP-B/SP-C (2:1, w/w) to remove phospholipid during squeeze-out from their mixed films with DPPG. The effects of Ca2+ on the monolayers of DPPG plus hydrophobic surfactant proteins were consistent with calcium producing diminished lipid-protein interactions, possibly resulting from Ca(2+)-induced changes in the ionization state and molecular packing of DPPG.
Taneva
S G
SG
Department of Biochemistry, Memorial University of Newfoundland, St. John's, Canada.
Keough
K M
KM
D015060:1,2-Dipalmitoylphosphatidylcholine; D000388:Air; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent; D010715:Phosphatidylglycerols; D010743:Phospholipids / Q000737:chemistry*; D011312:Pressure; D011510:Proteolipids / Q000737:chemistry*; D011663:Pulmonary Surfactants / Q000737:chemistry*; D013552:Swine; D014867:Water
D002413:Cations, Divalent; D010715:Phosphatidylglycerols; D010743:Phospholipids; D011510:Proteolipids; D011663:Pulmonary Surfactants; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine; D002118:Calcium; C030345:1,2-dipalmitoylphosphatidylglycerol