Brancaleon L, Crippa P R, Diemmi D
Dipartimento di Fisica, Università di Parma, Viale delle Scienze, 43100 Parma, Ilalia.
Biopolymers. 1995 Dec;36(6):723-33. doi: 10.1002/bip.360360606.
The photophysics of Trp-containing peptides is extremely affected by the position of the indole ring with respect to substituents. In this work an unusual temperature fluorescence quenching behavior is presented. The N-tryptophan terminal peptides (N-Trp) show an increase of the static emission intensity as rising the temperature from 10 to about 40 degrees C. the anomaly is typical of the N-Trp terminal peptides since neither tryptophan (Trp) nor glycyl-tryptophan (Gly-Trp) and alanyl-tryptophan (Ala-Trp) show the same trend; a similar behavior is not detected in the C-tryptophan terminals. The other important features are the wavelength and pH dependence of the effect. The anomaly is in fact detected only at neutral pH and for excitation wavelength near the red edge of the UVB absorption band of indole. An interpretation of the anomaly is suggested, though more sophisticated techniques are needed to better focus the problem; the model proposed involves the superimposition of a ground state effect (the temperature-induced equilibrium shift from the zwitterionic to the anionic form of the peptides) and an excited state mechanism. At present no unique interpretation can be provided about the excited state mechanism that favors the anomaly ans some suggestions are discussed.
含色氨酸肽的光物理性质极易受到吲哚环相对于取代基位置的影响。在这项工作中，呈现了一种不寻常的温度荧光猝灭行为。N - 色氨酸末端肽（N - Trp）在温度从10℃升至约40℃时，静态发射强度会增加。这种异常是N - Trp末端肽所特有的，因为色氨酸（Trp）、甘氨酰 - 色氨酸（Gly - Trp）和丙氨酰 - 色氨酸（Ala - Trp）均未表现出相同趋势；在C - 色氨酸末端未检测到类似行为。其他重要特征是该效应的波长和pH依赖性。实际上，这种异常仅在中性pH以及吲哚UVB吸收带红边附近的激发波长下才能检测到。尽管需要更复杂的技术来更好地聚焦该问题，但还是对这种异常提出了一种解释；所提出的模型涉及基态效应（温度诱导的肽从两性离子形式向阴离子形式的平衡转变）和激发态机制的叠加。目前，对于有利于这种异常的激发态机制无法给出唯一的解释，并讨论了一些建议。
