Buchko G W, Rozek A, Hoyt D W, Cushley R J, Kennedy M A
Pacific Northwest National Laboratories, Environmental Molecular Sciences Laboratory, Richland, WA 99352, USA.
Biochim Biophys Acta. 1998 May 20;1392(1):101-8. doi: 10.1016/s0005-2760(98)00028-9.
Pulsed-field-gradient NMR spectroscopy was used to measure translational diffusion coefficients (Ds) for a peptide corresponding to a proposed lipid-binding domain of human apolipoprotein C-I, residues 7-24 (apoC-I(7-24)). Diffusion coefficients for apoC-I(7-24) were determined directly by following the decay of the resonance intensity of selected peptide protons at various concentrations of sodium dodecyl sulfate (SDS), a detergent increasingly being used to model the apolipoprotein environment. Previously, diffusion coefficients of peptides in the presence of SDS have been determined indirectly by monitoring the SDS diffusion coefficient. The direct measurement of the diffusion coefficient of the peptide enables one to distinguish whether SDS simply coats the peptide's surface to produce a uniformly charged 'rod' or if the peptide associates with a micelle. Using the direct method, at SDS concentrations above 5 mM (which is below the SDS critical micelle concentration (8.1 mM)), apoC-I(7-24) exhibited diffusion coefficients consistent with the formation of a large-molecular-weight complex. Based on the ratio of the diffusion coefficients for free- and SDS-associated peptide, the molecular weight of the peptide-SDS complex was much larger than a factor of 1. 4, the increase in molecular weight of the free peptide predicted if apoC-I(7-24) was uniformly surface coated with SDS.
脉冲场梯度核磁共振光谱法用于测量一种对应于人载脂蛋白C-I拟脂质结合结构域(第7至24位氨基酸残基,apoC-I(7-24))的肽段的平移扩散系数(Ds)。通过跟踪在不同浓度十二烷基硫酸钠(SDS)存在下选定肽段质子的共振强度衰减,直接测定apoC-I(7-24)的扩散系数,SDS是一种越来越多地用于模拟载脂蛋白环境的去污剂。此前,肽段在SDS存在下的扩散系数是通过监测SDS扩散系数间接测定的。直接测量肽段的扩散系数能够区分SDS是仅仅覆盖肽段表面以产生均匀带电的“棒状物”,还是肽段与胶束缔合。使用直接法,在SDS浓度高于5 mM(低于SDS临界胶束浓度8.1 mM)时,apoC-I(7-24)表现出与形成大分子复合物一致的扩散系数。基于游离肽段和与SDS结合的肽段的扩散系数之比,肽段-SDS复合物的分子量远大于1.4倍,1.4倍是如果apoC-I(7-24)被SDS均匀覆盖在表面时游离肽段预测的分子量增加倍数。