PHOSPHOLIPID PACKING ASYMMETRY IN CURVED MEMBRANES DETECTED BY FLUORESCENCE SPECTROSCOPY
PHOSPHOLIPID PACKING ASYMMETRY IN CURVED MEMBRANES DETECTED BY FLUORESCENCE SPECTROSCOPY
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DOI：
10.1021/bi00359a057
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发表时间：
1986-06-03
期刊：
影响因子：
2.9
通讯作者：
BRAMHALL, J
中科院分区：
文献类型：
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作者：
BRAMHALL, J
磷脂分子在小脂质囊泡的内膜和外膜单层中的分子堆积存在明显差异;小曲率半径赋予这两个单层之间的界面不对称性。我已经使用了两亲性荧光探针，N-[5-（二甲氨基）萘基-1-磺酰基]甘氨酸（dansylglycine），以确定这种不对称的分子包装是否导致存在不同的环境中的荧光探针驻留在膜。丹酰甘氨酸对环境的介电常数高度敏感，膜结合染料的荧光信号与水介质中的荧光信号相距较远。当丹酰甘氨酸第一次与囊泡混合时，它迅速分配到外层单层中;随后染料移动到内层单层中要慢得多。由于初始分配和随后的易位之间的时间滞后，因此可以测量易位前后膜结合染料的发射光谱，从而区分丹磺酰甘氨酸分子的两种潜在环境。在小的二棕榈酰磷脂酰胆碱囊泡的外膜单层中，染料荧光发射在530 nm处最大，对应于荧光团周围介质的介电常数为7。对于内单层中的染料，发射在519 nm处最大，对应于4.7的介电常数。结果表明，水分子被排除更有效地从染料结合位点的内膜单层比他们是从那些外单层。当对具有非常大的曲率半径的囊泡进行类似的测量时，位于外单层或内单层的染料的最大发射波长没有可检测到的差异，这两个位置都产生约535 nm的发射，对应于介电常数10。因此，它似乎是在小脂质囊泡的磷脂包装几何外膜单层密切平行的平面胆汁。与此相反，内部单层似乎受到包装的限制，独特的曲率半径小的系统。
There are distinct differences in the molecular packing of phospholipid molecules in the inner and outer membrane monolayers of small lipid vesicles; a small radium of curvature imparts an asymmetry to the interface between these two monolayers. I have used an amphiphilic fluorescent probe, N-[5-(dimethylamino)naphthalenyl-1-sulfonyl]glycine (dansylglycine), to determine if this asymmetry in molecular packing leads to the existence of different environments for fluorescent probes resident in the membrane. Dansylglycine is highly sensitive to the dielectric constant of its environment, and the fluorescence signal from membrane-bound dye is distant from that in the aqueous medium. When dansylglycine is first mixed with vesicles, it rapidly partitions into the outer monolayer; the subsequent movement of dye into the inner monolayer is much slower. Because of the time lag between the initial partitioning and the subsequent translocation, it is possile to measure the emission spectrum from membrane-bound dye before and after translocation, thus distinguishing the two potential environments for dansylglycine molecules. In the outer membrane monolayer of small dipalmitoylphosphatidylcholine vesicles, dye fluorescence emission is maximal at 530 nm, corresponding to a dielectric constant of 7 for the medium surrounding the fluorophore. For dye in the inner monolayer, emission is maximal at 519 nm, corresponding to a dielectric constant of 4.7. The results suggest that water molecules are excluded more efficiently from the dye binding sites of the inner membrane monolayer than they are from those of the outer monolayer. When similar measurements were made on vesicles with a very large radius of curvature, there was no detectable difference in the wavelength of maximal emission from dye located in the outer or inner monolayers, both locations giving rise to emission at approximately 535 nm, corresponding to a dielectric constant of 10. Thus, it seems that in small lipid vesicles the phospholipid packing geometry of the outer membrane monolayer closely parallels that of a planar bilary. In contrast, the inner monolayer appears to be subjected to packing constraints unique to systems with small radius of curvature.