Institute of Physics, Autonomous University of San Luis Potosi, Alvaro Obregón 64, 78000 San Luis Potosí, S.L.P., México.
J Phys Chem B. 2009 Dec 31;113(52):16547-56. doi: 10.1021/jp907443x.
Langmuir films of globulin 11S protein, l-dipalmitoylphosphatidylcholine (L-DPPC), and mixtures of both on water and on buffer subphases were studied. Brewster angle microscopy (BAM) was used to characterize in situ the films morphology along Pi-A isotherms at the air/liquid interface. The L-DPPC monolayer on water behaved as has been reported extensively in the literature but a slight increase on surface pressure and a notable change in domain morphology is observed on buffer. This difference in domain behavior is due to the stabilization interaction of the LE phase by the buffer ions. On the other hand, the protein monolayer was prepared by direct deposit or injection below the surface. Both methods formed mostly a condensed film, with a multilayer formed by globular aggregates in the first method with the two subphases. However, the second method showed different behavior of the protein films depending on the subphase; on water the protein formed a homogeneous film with some globule aggregates, but on buffer a remarkably well-organized monolayer was observed by atomic force microscopy (AFM). Mixtures of globulin 11S and L-DPPC were prepared using both methods for the protein film formation at the air/fluid interface. BAM showed that the mixtures formed coexistence regions between two condensed phases, whose domains of both phases behave like liquids. Fingering phenomena were observed at the interface between protein-rich and L-DPPC-rich domains, which indicates that both phases are fluid. AFM images of the mixtures show the formation of protein- or L-DPPC-rich domains. The liquidlike behavior could be explained due to different sizes of the protein and the L-DPPC, the minority compound in each kind of domain produces defects making them behave as liquids. Interestingly enough, as the monolayer is compressed to higher surface pressure, the lipid molecules are squeezed out and complete separation of the protein and L-DPPC is produced. Furthermore, we present evidence that the protein/L-DPPC mixtures produce films with holes, which might indicate its tendency to form hollow aggregates that could have some relevance in water-channel formation for in vivo seed germination.
球蛋白 11S 蛋白、L-二月桂酰基磷脂酰胆碱（L-DPPC）及其混合物在水相和缓冲亚相上的朗缪尔膜进行了研究。使用布鲁斯特角显微镜（BAM）原位表征了在空气/液体界面沿 Pi-A 等温线的膜形态。在水相上的 L-DPPC 单层的行为与文献中广泛报道的行为一致，但在缓冲相上观察到表面压力略有增加和畴形态发生明显变化。这种畴行为的差异是由于缓冲离子对 LE 相的稳定相互作用。另一方面，蛋白质单层是通过直接沉积或注射到表面以下制备的。两种方法都形成了主要是凝聚膜，在第一种方法中，与两种亚相一起形成了由球形聚集体组成的多层膜。然而，第二种方法显示了蛋白质膜的不同行为取决于亚相；在水相中，蛋白质形成了具有一些球形聚集体的均匀膜，但在缓冲相中，原子力显微镜（AFM）观察到了非常有序的单层。球蛋白 11S 和 L-DPPC 的混合物是通过两种方法制备的，用于在空气/流体界面上形成蛋白质膜。BAM 表明混合物形成了两个凝聚相之间的共存区域，两相的畴都表现为液体。在富含蛋白质和富含 L-DPPC 的畴之间的界面上观察到指状现象，这表明两相都是流体。混合物的 AFM 图像显示了蛋白质或 L-DPPC 富域的形成。液态行为可以解释为由于蛋白质和 L-DPPC 的大小不同，每种类型的域中的少数化合物产生缺陷，使它们表现为液体。有趣的是，随着单层被压缩到更高的表面压力，脂质分子被挤出，蛋白质和 L-DPPC 完全分离。此外，我们提供了证据表明，蛋白质/L-DPPC 混合物形成具有孔的膜，这可能表明其形成空心聚集体的趋势，这可能与体内种子发芽的水通道形成有关。
