Engelke M, Bojarski P, Diehl H A, Kubicki A
Institute of Experimental Physics, University of Bremen, Germany.
J Membr Biol. 1996 Sep;153(2):117-23. doi: 10.1007/s002329900115.
The presence of proteins in lipid bilayers always decreases the excimer formation rate of pyrene and pyrene lipid analogues in a way that is related to the protein-to-lipid ratio. Energy transfer measurements from intrinsic tryptophans to pyrene have shown (Engelke et al., 1994), that in microsomal membranes, the excimer formation rate of pyrene and pyrene fatty acids is heterogeneous within the membrane plane, because a lipid layer of reduced fluidity surrounds the microsomal proteins. This study investigates whether of not liposomes prepared from egg yolk phosphatidylcholine with incorporated gramicidin A give results comparable to those from microsomal membranes. The results indicate that the influence of proteins on the lipid bilayer cannot be described by one unique mechanism: Small proteins such as gramicidin A obviously reduce the excimer formation rate by occupying neighboring positions of the fluorescent probe and thus decrease the pyrene collision frequency homogeneously in the whole membrane plane, while larger proteins are surrounded by a lipid boundary layer of lower fluidity than the bulk lipid. The analysis of the time-resolved tryptophan fluorescence of gramicidin A incorporated liposomes reveals, that the tryptophan quenching by pyrene is stronger for tryptophans located closely below the phospholipid headgroup region because of the pyrene enrichment in this area of the lipid bilayer.
脂质双分子层中蛋白质的存在总是会降低芘和芘脂质类似物的激基缔合物形成速率，其降低方式与蛋白质 - 脂质比有关。从内在色氨酸到芘的能量转移测量结果表明（恩格尔克等人，1994年），在微粒体膜中，芘和芘脂肪酸的激基缔合物形成速率在膜平面内是不均匀的，因为微粒体蛋白质周围环绕着流动性降低的脂质层。本研究调查了由掺入短杆菌肽A的蛋黄磷脂酰胆碱制备的脂质体是否能给出与微粒体膜相当的结果。结果表明，蛋白质对脂质双分子层的影响不能用一种独特的机制来描述：像短杆菌肽A这样的小蛋白质显然通过占据荧光探针的相邻位置来降低激基缔合物形成速率，从而在整个膜平面内均匀降低芘的碰撞频率，而较大的蛋白质则被一层流动性低于主体脂质的脂质边界层所包围。对掺入短杆菌肽A的脂质体的时间分辨色氨酸荧光分析表明，由于芘在脂质双分子层的该区域富集，位于磷脂头部基团区域正下方的色氨酸被芘淬灭的程度更强。
