Tank D W, Wu E S, Meers P R, Webb W W
Biophys J. 1982 Nov;40(2):129-35. doi: 10.1016/S0006-3495(82)84467-6.
We have measured the lateral diffusion coefficient (D), of active dansyl-labeled gramicidin C (DGC), using the technique of fluorescence photobleaching recovery, under conditions in which the cylindrical dimer channel of DGC predominates. In pure, hydrated, dimyristoylphosphatidylcholine (DMPC) multibilayers (MBL), D decreases from 6 X 10(-8) cm2/s at 40 degrees C to 3 X 10(-8) cm2/s at 25 degrees C, and drops 100-fold at 23 degrees C, the phase transition temperature (Tm) of DMPC. Above Tm, addition of cholesterol decreases D; a threefold stepwise drop occurs between 10 and 20 mol %. Below Tm, increasing cholesterol increases D; a 10-fold increase occurs between 10 and 20 mol % at 21 degrees C, between 20 and 25 mol % at 15 degrees C, and between 25 and 30 mol % at 5 degrees C. In egg phosphatidylcholine (EPC) MBL, D decreases linearly from 5 X 10(-8) cm2/s at 35 degrees C to 2 X 10(-8) cm2/s at 5 degrees C; addition of equimolar cholesterol reduces D by a factor of 2. Thus this transmembrane polypeptide at low membrane concentrations diffuses quite like a lipid molecule. Its diffusivity in lipid mixtures appears to reflect predicted changes of lateral composition. Increasing gramicidin C (GC) in DMPC/GC MBL broadened the phase transition, and the diffusion coefficient of the lipid probe N-4-nitrobenzo-2-diazole phosphatidylethanolamine (NBD-PE) at 30 degrees C decreases from 8 X 10(-8) cm2/s below 5 mol % GC to 2 X 10(-8) cm2/s at 14 mol % GC; D for DGC similarly decreases from 4 X 10(-8) cm2/s at 2 mol % GC to 1.4 X 10(-8) cm2/s at 14 mol % GC. Hence, above Tm, high concentrations of this polypeptide restrict the lateral mobility of membrane components.
我们采用荧光光漂白恢复技术，在短杆菌肽C（DGC）的圆柱二聚体通道占主导的条件下，测量了活性丹磺酰标记的短杆菌肽C（DGC）的横向扩散系数（D）。在纯的、水合的二肉豆蔻酰磷脂酰胆碱（DMPC）多层膜（MBL）中，D在40℃时从6×10⁻⁸cm²/s降至25℃时的3×10⁻⁸cm²/s，并在23℃（DMPC的相变温度（Tm））时下降100倍。在Tm以上，添加胆固醇会降低D；在10至20摩尔%之间会出现三倍的逐步下降。在Tm以下，增加胆固醇会增加D；在21℃时，在10至20摩尔%之间增加10倍，在15℃时在20至25摩尔%之间增加，在5℃时在25至30摩尔%之间增加。在鸡蛋磷脂酰胆碱（EPC）MBL中，D从35℃时的5×10⁻⁸cm²/s线性下降至5℃时的2×10⁻⁸cm²/s；添加等摩尔胆固醇会使D降低一半。因此，这种跨膜多肽在低膜浓度下的扩散方式与脂质分子非常相似。其在脂质混合物中的扩散系数似乎反映了横向组成的预测变化。在DMPC/GC MBL中增加短杆菌肽C（GC）会拓宽相变，脂质探针N-4-硝基苯-2-重氮磷脂酰乙醇胺（NBD-PE）在30℃时的扩散系数从低于GC 5摩尔%时的8×10⁻⁸cm²/s降至GC 14摩尔%时的2×10⁻⁸cm²/s；DGC的D同样从GC 2摩尔%时的4×10⁻⁸cm²/s降至GC 14摩尔%时 的1.4×10⁻⁸cm²/s。因此，在Tm以上，高浓度的这种多肽会限制膜成分的横向流动性。
