Pauls K P, MacKay A L, Söderman O, Bloom M, Tanjea A K, Hodges R S
Eur Biophys J. 1985;12(1):1-11. doi: 10.1007/BF00254089.
The 2H-NMR spectrum of the exchangeable hydrogens of the synthetic amphiphilic polypeptide, lys2-gly-leu24-lys2-ala-amide, was measured for the solid peptide at room temperature and, as a function of temperature, for the peptide incorporated into hydrated dipalmitoylphosphatidylcholine (DPPC) bilayers. This study is a prototype of a similar class of experiments which can be carried out on integral membrane proteins to characterize, quantitatively, the dynamic properties of integral membrane proteins. At temperatures below the DPPC gel-liquid crystalline phase transition, the 2H NMR spectrum was very similar to that of the solid peptide indicating that the peptide was immobilized in the lipid bilayer on the time scale (approximately equal to 10(-5) s) of the 2H-NMR measurements. The 2H-NMR spectrum above the phase transition corresponded to that expected from a peptide in the alpha-helical conformation reorienting rapidly about the symmetry axis of the alpha-helix. Measurements of the quadrupolar echo relaxation time, T2e, gave a quantitative measure of the correlation time, tau c, for this motion. The value of tau c decreased rapidly with increasing temperature as the fraction of DPPC molecules in the liquid crystalline phase increased, reaching a value of 2 X 10(-7) s above the phase transition. The observation of a characteristic minimum in T2e as the temperature was raised provided a definitive, quantitative interpretation of the T2e measurements. Using the known geometry of the peptide and the theory of uniaxial rotational diffusion, a value of eta = 1.1 poise was obtained for the effective viscosity of the membrane in close agreement with values obtained previously from transient linear dichroism measurements.
在室温下测量了合成两亲性多肽lys2 - gly - leu24 - lys2 - ala - amide可交换氢的2H - NMR谱,并在不同温度下测量了掺入水合二棕榈酰磷脂酰胆碱(DPPC)双层中的该多肽的谱。本研究是可对整合膜蛋白进行的类似实验的一个范例,这些实验可用于定量表征整合膜蛋白的动态特性。在低于DPPC凝胶 - 液晶相转变温度时,2H NMR谱与固体多肽的谱非常相似,表明在2H - NMR测量的时间尺度(约等于10^(-5) s)上,多肽固定在脂质双层中。相变温度以上的2H - NMR谱与α - 螺旋构象的多肽绕α - 螺旋对称轴快速重排所预期的谱一致。四极回波弛豫时间T2e的测量给出了该运动相关时间τc的定量度量。随着液晶相中DPPC分子分数增加,τc值随温度升高而迅速降低,在相变温度以上达到2×10^(-7) s的值。随着温度升高,T2e出现特征性最小值,这为T2e测量提供了明确的定量解释。利用多肽已知的几何结构和单轴旋转扩散理论,得到膜有效粘度η = 1.1泊,这与先前从瞬态线性二色性测量获得的值非常一致。