Mannock David A, Benesch Matthew G K, Lewis Ruthven N A H, McElhaney Ronald N
Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Biochim Biophys Acta. 2015 Aug;1848(8):1629-38. doi: 10.1016/j.bbamem.2015.04.009. Epub 2015 Apr 22.
We performed comparative DSC and FTIR spectroscopic measurements of the effects of β-sitosterol (Sito) and stigmasterol (Stig) on the thermotropic phase behavior and organization of DPPC bilayers. Sito and Stig are the major sterols in the biological membranes of higher plants, whereas cholesterol (Chol) is the major sterol in mammalian membranes. Sito differs in structure from Chol in having an ethyl group at C24 of the alkyl side-chain, and Stig in having both the C24 ethyl group and trans-double bond at C22. Our DSC studies indicate that the progressive incorporation of Sito and Stig decrease the temperature and cooperativity of the pretransition of DPPC to a slightly lesser and greater extent than Chol, respectively, but the pretransition persists to 10 mol % sterol concentration in all cases. All three sterols produce essentially identical effects on the thermodynamic parameters of the sharp component of the DPPC main phase transition. However, the ability to increase the temperature and decrease the cooperativity and enthalpy of the broad component decreases in the order Chol>Sito>Stig. Nevertheless, at higher Sito/Stig concentrations, there is no evidence of sterol crystallites. Our FTIR spectroscopic studies demonstrate that Sito and especially Stig incorporation produces a smaller ordering of the hydrocarbon chains of fluid DPPC bilayers than does Chol. In general, the presence of a C24 ethyl group in the alkyl side-chain reduces the characteristic effects of Chol on the thermotropic phase behavior and organization of DPPC bilayer membranes, and a trans-double bond at C22 magnifies this effect.
我们进行了差示扫描量热法（DSC）和傅里叶变换红外光谱（FTIR）测量，以研究β-谷甾醇（Sito）和豆甾醇（Stig）对二棕榈酰磷脂酰胆碱（DPPC）双层膜热致相行为和结构的影响。Sito和Stig是高等植物生物膜中的主要甾醇，而胆固醇（Chol）是哺乳动物膜中的主要甾醇。Sito与Chol在结构上的不同在于其烷基侧链的C24位有一个乙基，而Stig在C24位有乙基且在C22位有反式双键。我们的DSC研究表明，Sito和Stig的逐步掺入分别使DPPC预转变的温度和协同性降低，程度略小于和大于Chol，但在所有情况下，预转变在甾醇浓度达到10 mol%时仍会持续。所有三种甾醇对DPPC主相转变尖锐成分的热力学参数产生的影响基本相同。然而，提高宽成分的温度、降低其协同性和焓变的能力按Chol>Sito>Stig的顺序递减。尽管如此，在较高的Sito/Stig浓度下，没有甾醇微晶的迹象。我们的FTIR光谱研究表明，与Chol相比，Sito尤其是Stig的掺入使流体DPPC双层膜的烃链有序度降低。一般来说，烷基侧链中C24位乙基的存在会降低Chol对DPPC双层膜热致相行为和结构的特征影响，而C22位的反式双键会放大这种影响。
