SPECTROSCOPIC AND IONIZATION PROPERTIES OF N-(7-NITROBENZ-2-OXA-1,3-DIAZOL-4-YL)-LABELED LIPIDS IN MODEL MEMBRANES
SPECTROSCOPIC AND IONIZATION PROPERTIES OF N-(7-NITROBENZ-2-OXA-1,3-DIAZOL-4-YL)-LABELED LIPIDS IN MODEL MEMBRANES
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DOI：
10.1016/0005-2736(88)90118-6
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发表时间：
1988-02-08
期刊：
影响因子：
--
通讯作者：
LONDON, E
中科院分区：
文献类型：
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作者：
CHATTOPADHYAY, A;LONDON, E
用荧光、吸光度和电泳迁移率测量方法研究了7-硝基苯-2-氧杂-1，3-二氮唑-4-基（NBD）标记的各种脂质在模型膜中的光谱和电离性质。电泳测量表明，NBD基团在中性pH下不带电荷。然而，在高pH下，羟基加成或去质子化发生，pKa取决于条件，对于头基标记的磷脂酰乙醇胺（NBD-PE）的NBD基团为11.5-11.8，对于位于磷脂酰胆碱的一个脂肪酰基链末端的NBD标记为11.1 - 11.5（6-NBD-PC和12-NBD-PC）。在将甲基化NBD标记置于胆固醇（NBD-胆固醇）的柔性“尾”中的情况下，未观察到这种类型的行为。NBD-PE和NBD-PC的pKa相似性表明，在这些情况下，NBD基团在膜中的深度相似。通过比较模型膜中NBD基团的荧光发射最大值与不同极性溶剂中的荧光发射最大值，进一步研究了这一点。NBD基团在模型膜中经历的表观极性表明，对于NBD-PE和12-NBD-PC，它们位于极性区域，而NBD-胆固醇的NBD基团深埋在膜的非极性区域中。测量NBD暴露于水性猝灭剂Co2+的荧光猝灭实验进一步支持该结论。本研究的结果证实了我们以前的荧光猝灭研究的NBD基团在模型膜中的位置的初步结论。
The spectroscopic and ionization properties of various lipids labeled with the 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) group have been studied in model membranes using fluorescence, absorbance and electrophoretic mobility measurements. Electrophoretic measurements show that the NBD group is uncharged at neutral pH. However, at high pH, hydroxyl addition or deprotonation occurs with a pKa, depending upon conditions, of 11.5-11.8 for the NBD group of headgroup-labeled phsophatidylethanolamine (NBD-PE) and 11.1 - 11.5 for NBD labels placed at the end of one fatty acyl chain of a phosphatidylcholine (6-NBD-PC and 12-NBD-PC). This type of behavior is not observed in the case of a methylated NBD label placed in the flexible ''tail'' of cholesterol (NBD-cholesterol). The similarity in pKa for NBD-PE and NBD-PCs suggests that in these cases the NBD group is at a similar depth in the membrane. This was examined further by comparison of the fluorescence emission maximum of the NBD group in model membranes with that in solvents of varying polarity. The apparent polarity experienced by NBD groups in model membranes indicates that for NBD-PE and 12-NBD-PC they are located at the polar region whereas the NBD group of NBD-cholesterol is deeply buried in a nonpolar region of the membrane. This conclusion is supported further by fluorescence quenching experiments measuring NBD exposure to the aqueous quencher Co2+. The results of this study confirm the tentative conclusions of our previous fluorescence quenching studies on the location of NBD groups in model membranes.