Kitagawa T, Nagai K
Nature. 1979 Oct 11;281(5731):503-4. doi: 10.1038/281503a0.
Spectroscopic studies have provided extensive information on the primary process of visual pigments and photoexcitation of chlorophyll as well as their effects on photoreactivity on the higher-order structures of protein has been observed only rarely. Resonance Raman spectroscopy can reveal the vibrational frequencies of the chromophore in a molecule provided the excitation wavelength is in the absorption band of that molecule. As the visible absorption bands of haemproteins are due to pi pi* transitions of the porphyrin ring, we can selectively observe the vibrational frequencies of iron porphyrin during in situ interactions with immediate amino acid residues of protein when the wavelength of excitation light is close to the Soret or Q band. Correlation of some vibrational frequencies of haem with the oxidation and spin states of the haem iron has been studied in detail and an empirical rules has been established. This method is therefore especially suitable for the study of an effect of higher-order structures of protein on the chromophore. We report here a photoreaction facilitated by a particular quaternary structure of protein--in various haemoglobins resonance Raman spectroscopy showed that reversible photoreduction of haem took place in the T state but not the R state.
光谱研究已经提供了关于视觉色素的初级过程、叶绿素的光激发以及它们对蛋白质高阶结构光反应性的影响等广泛信息，但关于后者的研究却很少。共振拉曼光谱能够揭示分子中生色团的振动频率，前提是激发波长处于该分子的吸收带内。由于血红素蛋白的可见吸收带是由于卟啉环的π→π*跃迁所致，当激发光波长接近Soret带或Q带时，我们能够在原位观察铁卟啉与蛋白质紧邻氨基酸残基相互作用时的振动频率。已经详细研究了血红素的一些振动频率与血红素铁的氧化态和自旋态之间的相关性，并建立了经验规则。因此，该方法特别适用于研究蛋白质高阶结构对生色团的影响。我们在此报告一种由蛋白质特定四级结构促进的光反应——在各种血红蛋白中，共振拉曼光谱表明，血红素的可逆光还原发生在T态而非R态。
