Ultraviolet Resonance Raman Spectroscopic Study on the Conformation of Enkephalin and Binding Mode to Receptors

我们研究了二月桂酰磷脂酰胆碱脂质体中甲硫氨酸脑啡肽、亮氨酸脑啡肽和[Trp ^4]甲硫氨酸脑啡肽的紫外（213和240 nm）共振拉曼（UVRR）光谱。根据先前获得的模型化合物的数据的光谱的分析提供了几条重要的信息，脑啡肽的结合模式的脂质双层。从大鼠脑中提取并纯化了δ型阿片受体。用紫外吸收光谱和圆二色光谱研究了受体的结构。主要研究结果如下：1.上述脑啡肽在水溶液中均以各种伸展构象的集合体形式存在，而在脂结合态则以折叠构象存在. Tyr侧链插入到膜疏水内部，而Phe侧链位于极性表面区域或暴露于水相. Tyr插入膜的程度Leu-脑啡肽比其他两种小. Tyr埋得越深，肽的亲和力和活性越高.膜环境被认为在保护N-末端Tyr免于在组织中降解方面起作用.δ-阿片受体的主链主要是β-折叠结构，并且蛋白质不含许多芳香族残基，特别是Tyr和Typ。

We have studied the ultraviolet (213- and 240-nm) resonance Raman (UVRR) spectra of Met-enkephalin, Leu-enkephalin, and [Trp^4] Met-enkephalin incorporated into dilauroylphatidylcholine liposomes. The analysis of the spectra based on the data of model compounds obtained previously has provided several pieces of important information on the binding mode of enkephalin to the lipid bilayers. A delta-type opioid receptor has been extracted from rat brain and purified. The structure of the receptor has been investigated by UVRR and circular dichroism spectroscopy. The results obtained are as follows :1. Every enkephalin mentioned above exists as an ensemble of various extended conformers in aqueous solution, whereas it takes a folded conformation in the lipid-bound state.2. The Tyr side chain is inserted into the membrane hydrophobic interior, but the Phe side chain is located in the polar surface region or exposed to the aqueous phase.3. The degree of insertion of Tyr into the membrane is smaller for Leu-enkephalin than the other two.4. The deeper the Tyr is buried, the higher the affinity and activity of the peptide.5. The membrane environment is considered to play a role in protecting the N-terminal Tyr form degradation in tissues.6. The mainchain of the delta-opioid receptor is largely in the beta-sheet structure and the protein does not contain many aromatic residues, particularly Tyr and Typ.