Dhand R, Sharma V K, Teng A L, Krishnasamy S, Gross N J
Division of Pulmonary and Critical Care Medicine, Edward Hines Jr. Veterans Affairs Hospital, Hines, Illinois, USA.
Biochem Biophys Res Commun. 1998 Mar 27;244(3):712-9. doi: 10.1006/bbrc.1998.8325.
Surfactant convertase is required for conversion of heavy density (H) natural surfactant to light density (L) subtype during cycling in vitro, a technique that reproduces surfactant metabolism. To study mechanisms of H to L conversion, we prepared liposomes of dipalmitoylphosphatidylcholine (DPPC) and phosphatidylglycerol (PG), or the phospholipids (PL) in combination with either surfactant protein A (SP-A), surfactant protein B (SP-B), or both SP-A and SP-B. Phospholipids alone showed time-dependent conversion from heavy to light subtype on cycling in the absence of convertase, which was decreased by adding SP-B, but not SP-A, to phospholipids (p < 0.01 for PL+SP-B, or PL+SP-A+SP-B vs. PL, or PL+SP-A). The ultrastructure, surface activity, buoyant density, and L subtype generation on cycling PL+SP-A+SP-B with partially purified convertase or with phospholipase D were similar to those of natural TM. In conclusion, a reconstituted surfactant mimics the behavior of natural surfactant on cycling, and reveals that interaction of SP-B with phospholipids decreases L subtype generation. In addition, esterase/ phospholipase D activity is required for conversion of heavy to light subtype on cycling.
在体外循环过程中，表面活性剂转化酶是将高密度（H）天然表面活性剂转化为低密度（L）亚型所必需的，体外循环是一种重现表面活性剂代谢的技术。为了研究H向L转化的机制，我们制备了二棕榈酰磷脂酰胆碱（DPPC）和磷脂酰甘油（PG）的脂质体，或者将磷脂（PL）与表面活性剂蛋白A（SP-A）、表面活性剂蛋白B（SP-B）或SP-A和SP-B两者结合。单独的磷脂在没有转化酶的情况下循环时显示出从重亚型到轻亚型的时间依赖性转化，在磷脂中添加SP-B而不是SP-A可降低这种转化（PL+SP-B或PL+SP-A+SP-B与PL或PL+SP-A相比，p<0.01）。用部分纯化的转化酶或磷脂酶D对PL+SP-A+SP-B进行循环时，其超微结构、表面活性、浮力密度和L亚型生成与天然TM相似。总之，重构的表面活性剂在循环时模拟天然表面活性剂的行为，并揭示SP-B与磷脂的相互作用会减少L亚型的生成。此外，酯酶/磷脂酶D活性是循环时从重亚型转化为轻亚型所必需的。
