Cholesterol-phospholipid interaction in membranes. 1. Cholestane spin-label studies of phase behavior of cholesterol-phospholipid liposomes.
Cholesterol-phospholipid interaction in membranes. 1. Cholestane spin-label studies of phase behavior of cholesterol-phospholipid liposomes.
复制标题
膜中胆固醇-磷脂的相互作用。
DOI：
10.1021/bi00259a016
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发表时间：
1982
期刊：
影响因子：
2.9
通讯作者：
Chan,SI
中科院分区：
文献类型：
--
作者：
Presti,FT;Chan,SI
表一：低（PRE）主^中点13-13.5 34 " 41.4 " AT, n 1.0 2 " 0.25 b isH (kcal/mol) 2.6±0.4 b 1.0±0.2 b 8.4±0.3 b AF (uL/g) 9.0±0.5 3.3±0.5 " 35±1 " AT /ydw (kcal/mol) 1.5-1.8 0.5-0.6 5.5 " " Nagle & Wilkinson（1978）。b这项工作，但参见Chen等人（1980）的值范围。0从图2的导数与量热半宽度的比较。图2的膨胀半宽度为0.6 c，表1给出了在内部范德华力作用下，膨胀双层烃链部分所需能量的估计，假设整个测量的膨胀发生在烃链区域。计算基本上遵循前面详细描述的主要转变（Nagle & Wilkinson, 1978）。表1中给出的A£/vdW的取值范围（包括子跃迁和下跃迁）源于处理排斥相互作用的两种不同方法。表1中较低的值是通过保留Salem（1962）公式中较不精确的排斥项而得出的。然而，如果这些转变中的任何一种涉及到任何明显的碳氢链的取向或堆叠顺序，那么就需要进行更精确的计算。这样的排序似乎会减少At/^ w的负排斥部分。表1中较大的A£/vdw值是通过完全忽略相互作用的排斥部分来计算的。在任何情况下，AI/vdW安全地小于AH，但仍然是AH的重要组成部分。
Table I: Equilibrium Thermodynamic Phase Transition Properties of DPPC transitions sub lower (PRE) main^ midpoint 13-13.5 34 “ 41.4 “AT, n 1.0 2 “ 0.25 b isH (kcal/mol) 2.6±0.4 b 1.0±0.2 b 8.4±0.3 b AF (uL/g) 9.0±0.5 3.3±0.5 “ 35±1 “At/ydw (kcal/mol) 1.5-1.8 0.5-0.6 5.5 ““Nagle & Wilkinson (1978). b This work, but see Chen et al.(1980) for range of values. 0 From the derivative of Figure 2 for comparison with calorimetric half-widths. The dilatometric half-width from Figure 2 is 0.6 C. of Table I gives estimates of the energy required to expand the hydrocarbon chain portion of the bilayer against internal van der Waals forces, assuming that the entire measured expansion occurs in the hydrocarbon chain region. The cal-culation essentially follows the one described in detail earlier (Nagle & Wilkinson, 1978) for the main transition. Therange of values of A£/vdW presented in Table I (for both the sub-transition and the lowertransition) arises from two different ways of treating the repulsive interactions. The lower values in Table I are derived by retaining the less accurate repulsive term in the formulaof Salem (1962). However, if either of these transitions involves any appreciable orientational or stacking ordering of the hydrocarbon chains with respect to one another, then a more refined calculation is in order. Such ordering would appear to reduce the negative repulsive part of At/^ w The larger values of A£/vdw in Table I are calculated by ignoring the repulsivepart of the interaction completely. In any case AI/vdW is safely smaller than, butstill a significant fraction of, AH.