Effect of the hydrophobic surfactant proteins on the surface activity of spread films in the captive bubble surfactometer |
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Authors: | Veldhuizen E J Diemel R V Putz G van Golde L M Batenburg J J Haagsman H P |
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Affiliation: | Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine, Institute of Biomembranes and Graduate School of Animal Health, Utrecht University, P.O. Box 80176, 3508 TD, Utrecht, The Netherlands. |
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Abstract: | The main function of pulmonary surfactant, a mixture of lipids and proteins, is to reduce the surface tension at the air/liquid interface of the lung. The hydrophobic surfactant proteins SP-B and SP-C are required for this process. When testing their activity in spread films in a captive bubble surfactometer, both SP-B and SP-C showed concentration dependence for lipid insertion as well as for lipid film refinement. Higher activity in DPPC refinement of the monolayer was observed for SP-B compared with SP-C. Further differences between both proteins were found, when subphase phospholipid vesicles, able to create a monolayer-attached lipid reservoir, were omitted. SP-C containing monolayers showed gradually increasing minimum surface tensions upon cycling, indicating that a lipid reservoir is required to prevent loss of material from the monolayer. Despite reversible cycling dynamics, SP-B containing monolayers failed to reach near-zero minimum surface tensions, indicating that the reservoir is required for stable films. |
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