FLUORESCENCE, POLARIZED FLUORESCENCE, AND BREWSTER-ANGLE MICROSCOPY OF PALMITIC ACID AND LUNG SURFACTANT PROTEIN-B MONOLAYERS

Fluorescence, polarized fluorescence, and Brewster angle microscopy re veal that human lung surfactant protein SP-B and its amino terminus (S P-B1-25) alter the phase behavior of palmitic acid monolayers by inhib iting the formation of condensed phases and creating a new fluid prote in-rich phase. This fluid phase forms a network that separates condens ed phase domains at coexistence and persists to high surface pressures . The network changes the monolayer collapse mechanism from heterogene ous nucleation/growth and fracturing processes to a more homogeneous p rocess through isolating individual condensed phase domains. This resu lts in higher surface pressures at collapse, and monolayers easier to respread on expansion, factors essential to the in vivo function of lu ng surfactant. The network is stabilized by a low-line tension between the coexisting phases, as confirmed by the observation of extended li near domains, or ''stripe'' phases, and a Gouy-Chapman analysis of pro tein-containing monolayers. Comparison of isotherm data and observed m orphologies of monolayers containing SP-B1-25 with those containing th e full SP-B sequence show that the shortened peptide retains most of t he native activity of the full-length protein, which may lead to cheap er and more effective synthetic replacement formulations.