The interpretation of the UV absorption spectra of proteins was a matter of intense debate in the second half of the last century. The study of the spectroscopic characteristics of peptide bonds in proteins was then of particular interest but the absorption of a large number of peptide bonds in a protein is a complex subject which gathers many contributions such as those from other amino acid residues that absorb as well and therefore unequivocal proofs remains a challenge. This probably becomes the reason for being an almost untouched subject of study in the last 40 years or so.

In this report the spectroscopic characteristics of the amyloid disordered protein α-synuclein (Syn) were studied in detail, concerning the UV absorption spectra in the peptide bond (200–230 nm) and the aromatic regions. Several protein concentrations, several solution pH and the first 300 min of the aggregation reaction were here investigated.

In what the peptide bond region of Syn is concerned, UV difference spectra for a 33.5 μM protein solution concentration, in particular, revealed that at Syn solutions pH 7, 3 and 2 the counter-ion concentration increases in that order, as expected, accounting for the decrease of the peptide bond absorbance. Also, for this protein solution concentration, quantitative information can be obtained from peptide bond absorption and counter-ion concentration interplay in what the progression of the Syn aggregation reaction is concerned. This situation represents a label-free analysis of Syn aggregation in the lag-phase, in particular.

Concerning the aromatic region of Syn, the UV absorption spectra revealed a perturbation at ca. 290–310 nm which is not related with light scattering effects in the UV absorption spectra but is related with the formation of mostly intermolecular hydrogen-bonded complexes between Syn tyrosyl groups and aspartic and glutamic acids residues. Interestingly, is the possible enrollment of these intermolecular complexes in the stabilization of this highly dynamic disordered protein in solution.

蛋白质的紫外线吸收光谱的解释在上个世纪下半叶引起了激烈的争论。蛋白质中肽键的光谱特征的研究于是引起了特别的兴趣，但是蛋白质中大量肽键的吸收是一个复杂的课题，它吸引了许多贡献，例如来自其他氨基酸残基的吸收以及吸收。因此，明确的证明仍然是一个挑战。这可能成为过去40年来成为几乎未触及的研究主题的原因。

在本报告中，对淀粉样蛋白紊乱的蛋白质α-突触核蛋白（Syn）的光谱特性进行了详细研究，涉及肽键（200–230 nm）和芳香区域中的紫外线吸收光谱。在此研究了几种蛋白质浓度，几种溶液的pH值以及聚集反应的前300分钟。

就Syn的肽键区域而言，对于33.5μM蛋白溶液浓度的UV差异光谱尤其显示，在pH 7、3和2的Syn溶液中，抗衡离子浓度按预期的顺序增加。降低肽键吸收率。同样，对于这种蛋白质溶液浓度，可以从肽键吸收和抗衡离子浓度相互作用中获得有关Syn聚合反应进程的定量信息。这种情况尤其表示在滞后阶段对Syn聚合进行无标记分析。

关于Syn的芳族区域，UV吸收光谱显示出大约在200的扰动。290-310 nm与紫外线吸收光谱中的光散射效应无关，但与顺式酪氨酰基基团与天冬氨酸和谷氨酸残基之间大部分分子间氢键形成的络合物有关。有趣的是，这些分子间复合物可能参与了溶液中这种高度动态的无序蛋白的稳定化。