Department of Biochemistry, Temple University School of Medicine, 19140, Philadelphia, Pennsylvania.
J Fluoresc. 1996 Dec;6(4):221-30. doi: 10.1007/BF00732825.
Our previous studies indicated that sterols (including cholesterol and dehydroergosterol) can be regularly distributed into hexagonal superlattices in the plane of liquid-crystalline phosphatidylcholine bilayers. It was suggested that regular and irregular regions coexist in the membrane. In the present study, we report supporting evidence for our sterol regular distribution model. We have examined the fractional concentration dependencies of dehydroergosterol (a naturally occurring cholesterol analogue) fluorescence intensity and lifetime in various phosphatidylcholine and sphingomyelin bilayers. Fluorescence intensity and lifetime dips have been observed at specific sterol mole fractions. At those mole fractions, the acrylamide quenching rate constant of dehydroergosterol fluorescence reaches a local maximum. Those mole fractions match the critical sterol mole fractions at which sterol molecules are expected to be regularly distributed into hexagonal superlattices. The results support the idea that the sterols in the regular region are embedded in the bilayer less deep than those in the irregular regions. We have also examined the fractional cholesterol concentration dependencies of diphenylhexatriene (DPH) fluorescence intensity, lifetime, and polarization in DMPC vesicles. DPH fluorescence intensity and polarization also exhibit distinct dips and peaks, respectively, at critical sterol mole fractions for hexagonal superlattices. However, DPH lifetime changes little with sterol mole fraction. As a comparison, the fluorescence properties of DHE and DPH behave differently in response to the formation of sterol regular distribution. Furthermore, finding evidence for sterol regular distribution in both phosphatidylcholine and sphingomyelin membranes raises the possibility that sterol regular distribution may occur within phospholipid/cholesterol enriched domains of real biological membranes.
我们之前的研究表明，甾醇（包括胆固醇和脱氢麦角甾醇）可以在液晶磷脂双层膜的平面内规则地分布到六方超晶格中。有人提出，膜中同时存在规则区和不规则区。在本研究中，我们提供了支持甾醇规则分布模型的证据。我们研究了脱氢麦角甾醇（一种天然存在的胆固醇类似物）在各种磷脂酰胆碱和鞘磷脂双层膜中的荧光强度和寿命随分数浓度的依赖性。在特定的甾醇摩尔分数处观察到荧光强度和寿命的下降。在那些摩尔分数处，脱氢麦角甾醇荧光的丙烯酰胺猝灭速率常数达到局部最大值。这些摩尔分数与甾醇分子有望规则地分布到六方超晶格的临界甾醇摩尔分数相匹配。结果支持这样一种观点，即在规则区域的甾醇嵌入双层膜的深度小于不规则区域的甾醇。我们还研究了二苯基己三烯（DPH）在 DMPC 囊泡中的荧光强度、寿命和偏振随胆固醇分数依赖性。DPH 荧光强度和偏振也分别在六方超晶格的临界甾醇摩尔分数处表现出明显的下降和峰值。然而，DPH 寿命随甾醇摩尔分数的变化很小。相比之下，DHE 和 DPH 的荧光性质对甾醇规则分布的形成表现出不同的响应。此外，在磷脂酰胆碱和鞘磷脂膜中都发现甾醇规则分布的证据，这增加了甾醇规则分布可能发生在真实生物膜中富含磷脂/胆固醇的区域的可能性。
