Genz A, Holzwarth J F, Tsong T Y
Biophys J. 1986 Dec;50(6):1043-51. doi: 10.1016/S0006-3495(86)83548-2.
The influence of cholesterol (CHOL) on the main phase transition in single shell dipalmytoylphosphatidylcholine (DPPC) vesicles was investigated in equilibrium and kinetic experiments. CHOL increases the optical density and causes a slight hysteresis in turbidity transition curves. Static fluorescence anisotropy measurements showed interesting differences for three probes sensing different parts in the hydrophobic region of the phospholipid bilayer. Differential scanning calorimetry (DSC) peaks can be separated into a narrow and a broad component. The narrow component, which decreases linearly with increasing CHOL content and disappears at 20 mol %, is attributed to the transition of free phospholipid, while the broad component, being associated with the transition of CHOL-lipid units, increases monotoniously from 0 to 20%. Kinetic experiments were performed on our iodine-laser T-jump arrangement with turbidity detection. Three cooperative relaxation signals in the microsecond and millisecond time range were detected for pure DPPC vesicles as well as vesicles containing 7.5 and 16.5 mol % CHOL. All three relaxation processes were changed by CHOL: the superposition of the three relaxation amplitudes can be separated into a narrow and a broad component, as in DSC experiments. A speculative model is presented which assumes an inhomogeneous CHOL distribution fluctuating on a millisecond time scale in the temperature region of the main phase transition.
在平衡和动力学实验中，研究了胆固醇（CHOL）对单壳二棕榈酰磷脂酰胆碱（DPPC）囊泡主要相变的影响。胆固醇增加了光密度，并在浊度转变曲线中引起轻微的滞后现象。静态荧光各向异性测量显示，对于三种检测磷脂双层疏水区域不同部位的探针，存在有趣的差异。差示扫描量热法（DSC）峰可分为一个窄峰和一个宽峰。窄峰随胆固醇含量增加呈线性下降，并在20摩尔%时消失，归因于游离磷脂的转变；而与胆固醇-脂质单元转变相关的宽峰则从0%到20%单调增加。利用我们的碘激光T跳装置和浊度检测进行了动力学实验。对于纯DPPC囊泡以及含有7.5和16.5摩尔%胆固醇的囊泡，在微秒和毫秒时间范围内检测到三个协同弛豫信号。胆固醇改变了所有三个弛豫过程：与DSC实验一样，三个弛豫振幅的叠加可分为一个窄峰和一个宽峰。提出了一个推测模型，该模型假设在主要相变温度区域，胆固醇分布不均匀，在毫秒时间尺度上波动。
