Creuwels L A, van Golde L M, Haagsman H P
Laboratory of Veterinary Biochemistry, Utrecht University, The Netherlands.
Biochim Biophys Acta. 1996 Nov 13;1285(1):1-8. doi: 10.1016/s0005-2736(96)00131-9.
Pulmonary surfactant is a mixture of (phospho)lipids and surfactant specific proteins, lining the alveolar space. During each respiration cycle phospholipids are transferred between the phospholipid monolayer at the air/water interface and a variety of underlying membranes. Surfactant proteins may play a role in facilitating the insertion and removal of phospholipids by affecting the lipid organization of the bilayer and monolayer. The experiments described in this article were carried out in order to investigate the influence of surfactant protein B (SP-B) on the distribution of phospholipids in membranes and on the mixing of lipids between membranes. To determine the distribution of the non-labeled phospholipids in small unilamellar vesicles (SUV), the relative clustering of pyrene-labeled phospholipids was used, by measuring the ratio of excimer-to-monomer (E/M) pyrene fluorescence. In the absence of SP-B it was found that the clustering of the pyrenePC molecules was dependent on the proportion of saturated acyl chains and not on the proportion of negative charges. Addition of the positively charged SP-B to a mixture of DPPC and PG, led to an increase of approximately 20% in E/M ratio, indicating a clustering of the negatively charged PG molecules. This effect was intensified by addition of calcium ions. If pyrenePC-containing SUV were mixed with excess non-labeled SUV in the presence of SP-B and calcium ions, the E/M ratio decreased, corresponding with a flow of the pyrenePC molecules into the acceptor membranes. It is concluded that presence of domains of phospholipids can be detected with the use of pyrene-labeled phospholipids. Furthermore, SP-B showed a concentrating effect on the distribution of the negatively charged phospholipids, a process that could be important in regulating the phospholipid composition of the monolayer.
肺表面活性物质是一种由（磷酸）脂质和表面活性物质特异性蛋白质组成的混合物，覆盖在肺泡腔内。在每个呼吸周期中，磷脂在气/水界面的磷脂单分子层和各种下层膜之间转移。表面活性物质蛋白可能通过影响双层膜和单分子层的脂质组织，在促进磷脂的插入和去除过程中发挥作用。本文所述的实验旨在研究表面活性物质蛋白B（SP-B）对膜中磷脂分布以及膜间脂质混合的影响。为了确定小单层囊泡（SUV）中未标记磷脂的分布，通过测量芘标记磷脂的激基缔合物与单体（E/M）芘荧光的比率，来检测芘标记磷脂的相对聚集情况。在没有SP-B的情况下，发现芘标记的磷脂酰胆碱（pyrenePC）分子的聚集取决于饱和酰基链的比例，而不取决于负电荷的比例。向二棕榈酰磷脂酰胆碱（DPPC）和磷脂酰甘油（PG）的混合物中添加带正电荷的SP-B，导致E/M比率增加约20%，表明带负电荷的PG分子发生了聚集。添加钙离子会增强这种效应。如果在SP-B和钙离子存在的情况下，将含pyrenePC的SUV与过量的未标记SUV混合，E/M比率会降低，这与pyrenePC分子流入受体膜相对应。得出的结论是，可以使用芘标记的磷脂检测磷脂结构域的存在。此外，SP-B对带负电荷的磷脂分布表现出浓缩作用，这一过程在调节单分子层的磷脂组成方面可能很重要。
