Gauduchon P, Wahl P
Biophys Chem. 1975 Oct;3(4):317-22. doi: 10.1016/0301-4622(75)80024-x.
The fluorescence of cyclo-(glycyl-L-tryptophyl) in trimethyl phosphate has been studied in a temperature range varying from room temperature to -85 degrees C. At room temperature, the fluorescence decay is the sum of two exponentials, the relative amplitude of which depends on the emission wavelength. This can be explained by the presence of the two following emitting molecular states: on one hand the unfolded state, the fluorescence decay time and the emission spectrum of which are close to these of skatole; on the other hand the folded state which has a shorter decay time and a blue-shifted spectrum. By lowering the temperature, the fluorescence spectrum shifts to the blue, while the skatole spectrum shifts to the red. This behavior corresponds to an increase of the folded conformation concentration in agreement with the NMR results. Furthermore the rate of exchange between the folded and the unfolded conformations decreases. Accordingly the wavelength dependence of the fluorescence decay lessens. There are two possible values of the conformational angle x2 differing by 180 degrees, which correspond to the folded state; due to the indole asymmetry, the interactions between the indole and diketopiperazine rings differ in these conformers. Consequently the fluorescence decay remains biexponential even at -85 degrees C.
在从室温到 -85 摄氏度的温度范围内，对环（甘氨酰-L-色氨酰）在磷酸三甲酯中的荧光进行了研究。在室温下，荧光衰减是两个指数的总和，其相对幅度取决于发射波长。这可以通过以下两种发射分子状态的存在来解释：一方面是未折叠状态，其荧光衰减时间和发射光谱与粪臭素的相近；另一方面是折叠状态，其具有较短的衰减时间和蓝移光谱。通过降低温度，荧光光谱向蓝色移动，而粪臭素光谱向红色移动。这种行为与核磁共振结果一致，对应于折叠构象浓度的增加。此外，折叠态和未折叠态构象之间的交换速率降低。因此，荧光衰减的波长依赖性减弱。存在两个相差 180 度的构象角 x2 的可能值，它们对应于折叠状态；由于吲哚的不对称性，吲哚与二酮哌嗪环之间的相互作用在这些构象异构体中有所不同。因此，即使在 -85 摄氏度时，荧光衰减仍保持双指数形式。
