Wu J R, Lentz B R
Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill 27599-7260.
Biochemistry. 1991 Jul 9;30(27):6780-7. doi: 10.1021/bi00241a022.
Experiments were performed to assess three possible mechanisms of poly(ethylene glycol) (PEG) induced rapid lipid transfer between large unilamellar vesicles composed of dioleoylphosphatidylcholine: (1) transfer between aggregated vesicles, (2) transfer through an aqueous medium of lowered dielectric constant, and (3) transfer via a PEG carrier. The results showed that close contact between vesicles as a result of PEG dehydration was largely responsible for the rapid lipid transfer observed in the presence of PEG. The rate and extent of lipid transfer were also examined at 10 wt % PEG and analyzed in terms of a two-state model especially developed to account for the initial rate of lipid transfer as followed by the fluorescence lifetime of DPHpPC as a fluorescent lipid probe. Analysis revealed that two rate processes were involved in DPHpPC transfer between bilayers, both in the absence and presence of PEG. Since the maximum extent of transfer was 50%, transbilayer diffusion of DPHpPC seemed not to contribute to either process. The fast process in the presence of PEG was identified as due to rapid interbilayer monomer diffusion between closely apposed vesicles, and, in the absence of PEG, as due to monomer diffusion through the aqueous phase. The origin of the slow process, in both cases, remains obscure. The Arrhenius activation energies (and entropies) for the initial rates at temperatures from 10 to 48 degrees C were 15.3 +/- 0.3 kcal/mol (-26.3 +/- 0.2 eu) and 10.6 +/- 0.5 kcal/mol (-16.1 +/- 0.3 eu) in the absence and presence of PEG, respectively. The slow process was invariant with temperature.(ABSTRACT TRUNCATED AT 250 WORDS)
进行了实验以评估聚乙二醇（PEG）诱导由二油酰磷脂酰胆碱组成的大单层囊泡之间快速脂质转移的三种可能机制：（1）聚集囊泡之间的转移；（2）通过低介电常数水相介质的转移；（3）通过PEG载体的转移。结果表明，PEG脱水导致囊泡紧密接触在很大程度上是PEG存在时观察到的快速脂质转移的原因。还在10 wt% PEG下检查了脂质转移的速率和程度，并根据专门开发的双态模型进行分析，该模型用于解释脂质转移的初始速率，随后用DPHpPC作为荧光脂质探针的荧光寿命进行分析。分析表明，无论有无PEG，DPHpPC在双层之间的转移都涉及两个速率过程。由于最大转移程度为50%，DPHpPC的跨双层扩散似乎对这两个过程都没有贡献。PEG存在时的快速过程被确定为由于紧密相邻囊泡之间的快速双层间单体扩散，而在没有PEG时，是由于单体通过水相扩散。在这两种情况下，缓慢过程的起源仍然不清楚。在10至48摄氏度温度下，无PEG和有PEG时初始速率的阿伦尼乌斯活化能（和熵）分别为15.3±0.3 kcal/mol（-26.3±0.2 eu）和10.6±0.5 kcal/mol（-16.1±0.3 eu）。缓慢过程与温度无关。（摘要截断于250字）
