Kopple K D, Dickinson H R, Nakagawa S H, Flouret G
Biochemistry. 1976 Jul 13;15(14):2945-52. doi: 10.1021/bi00659a002.
The solution conformation of a retro-D analogue of tocinamide H-D-Cys-D-Asn-D-Gln-D-aIle-D-Tyr-NHCH2CH2S was examined using proton magnetic resonance and circular dichroism spectroscopy. The observations support major contributions to the conformational distribution from structures with a type I beta turn in the sequence D-Asp-D-Gln-D-aIle-D-Tyr. This is topologically similar to the beta turn proposed for oxytocin, L-Tyr-L-Ile-L-Gln-L-Asn, but with the polarity of the CONH groups reversed along the chain; the peptide is, however, hormonally inert. In conjuction with nuclear magnetic resonance data, the circular dichroism spectra are interpreted to indicate that the region of the peptide ring near the disulfide occurs in at least two different conformations. One of the side-chain carboxamides, probably that of asparagine, appears to be intramolecularly associated rather than freely exposed to solvent.
使用质子磁共振和圆二色光谱法研究了托西酰胺H-D-半胱氨酸-D-天冬酰胺-D-谷氨酰胺-D-丙氨酸-D-酪氨酸-NHCH2CH2S的反向D类似物的溶液构象。观察结果支持序列D-天冬氨酸-D-谷氨酰胺-D-丙氨酸-D-酪氨酸中具有I型β转角的结构对构象分布的主要贡献。这在拓扑结构上与催产素L-酪氨酸-L-异亮氨酸-L-谷氨酰胺-L-天冬酰胺提出的β转角相似，但CONH基团的极性沿链反转；然而，该肽在激素方面是无活性的。结合核磁共振数据，圆二色光谱被解释为表明肽环中靠近二硫键的区域至少以两种不同的构象存在。其中一个侧链羧酰胺，可能是天冬酰胺的，似乎是分子内缔合的，而不是自由暴露于溶剂中。
