Filippi B, Borin G, Moroder L, Marchiori F
Biochim Biophys Acta. 1976 Dec 13;454(3):524-38. doi: 10.1016/0005-2787(76)90278-1.
Far-ultraviolet difference absorption and circular dichroism (CD) spectra were recorded upon recombination of synthetic S-peptide analogs, i.e. 1epsilon, 7epsilon-diguanidino-[Tyr8]-, 1epsilon, 7epsilon-diguanidino-[Asn14]-, [Phe(F)8, Orn10]-, [Cha8, Orn10]- and 1epsilon, 7epsilon-diguanidono-S-peptide, with S-protein. The aromatic chromophores contributions to the absorption spectra in the 220-250 nm wavelengths interval strongly exceed the hyperchromism due to the random coil to right handled alpha-helix transition of the S-peptide, accompanying the association process. Contributions resulting from peptide transitions constitute a large portion of the total dichroism, nevertheless substitution of the non aromatic cycloexylalanine residue in position 8 of the S-peptide with phenylalanine, p-fluorophenylalanine and tyrosine leads to CD negative maxima located at 215, 215 and 212,5 nm, respectively. The strongest ellipticity increment (28%), relative to that of the Cha-derivative, was observed at 212,5 nm for the [Tyr8]-S-peptide analog, while in the narrow 222 nm range minimal differences were found upon insertion into the position 8 of the S-peptide of the above aromatic residues. Information derived from above data and from a comparison of RNAase A, S and S-protein CD spectra enabled us to assign the positive CD band at 240 nm in RNAase A spectrum to transitions of phenylalanines and inaccessible tyrosines.
在合成的S肽类似物，即1ε，7ε - 二胍基 - [Tyr8] - 、1ε，7ε - 二胍基 - [Asn14] - 、[Phe(F)8，Orn10] - 、[Cha8，Orn10] - 和1ε，7ε - 二胍基 - S肽与S蛋白重组时，记录了远紫外差吸收光谱和圆二色性（CD）光谱。在220 - 250nm波长区间内，芳香发色团对吸收光谱的贡献大大超过了S肽从无规卷曲向右手α - 螺旋转变所伴随的增色效应，该转变伴随着缔合过程。肽段转变产生的贡献在总二色性中占很大比例，然而，将S肽第8位的非芳香环己基丙氨酸残基分别用苯丙氨酸、对氟苯丙氨酸和酪氨酸取代后，导致CD负极大值分别位于215、215和212.5nm处。相对于Cha衍生物，[Tyr8] - S肽类似物在212.5nm处观察到最强的椭圆率增加（28%），而在222nm的狭窄范围内，将上述芳香残基插入S肽的第8位时差异最小。从上述数据以及核糖核酸酶A、S和S蛋白CD光谱的比较中获得的信息，使我们能够将核糖核酸酶A光谱中240nm处的正CD带归属于苯丙氨酸和不可及酪氨酸的跃迁。
