Tang S, MacColl R, Parsons P J
Department of Environmental Health and Toxicology, School of Public Health, State University of New York at Albany, USA.
J Inorg Biochem. 1995 Nov 15;60(3):175-85. doi: 10.1016/0162-0134(95)00018-j.
Transferrin is the plasma protein responsible for transporting Fe3+ from the absorption to the utilization site. Interactions of apo- and holo-transferrin with Al3+ were studied by circular dichroism (CD), UV-visible, and fluorescence spectrometry. Binding of Al3+ to both metal-ion binding sites of apo-transferrin was confirmed by fluorescence studies. No interaction of Al3+ with holo-transferrin was observed, indicating that Al3+ cannot displace Fe3+ under the experimental conditions employed. An increase in tryptophan fluorescence (lambda max at 330 nm) by excitation at either 280 or 295 nm was observed after Al3+ interaction with apo-transferrin. There was no shift in wavelength of the fluorescence band of apo-transferrin after interaction with Al3+, but the intensity did increase. Since excitation at 295 nm is specific for tryptophan residues, tryptophan but not tyrosine must be responsible for the change in fluorescence intensity. Decreased fluorescence is the result of Fe3+ binding to apo-transferrin. The CD spectrum of apo-transferrin was slightly affected in the far UV by Al3+ binding, but a salient change was noted in the near UV at approximately 288 nm where tyrosine and tryptophan absorb. It is concluded that a small conformational change in the protein was induced by Al3+ binding to apo-transferrin.
转铁蛋白是一种血浆蛋白，负责将Fe3+从吸收部位转运至利用部位。通过圆二色性（CD）、紫外可见光谱和荧光光谱研究了脱铁转铁蛋白和全铁转铁蛋白与Al3+的相互作用。荧光研究证实了Al3+与脱铁转铁蛋白的两个金属离子结合位点均有结合。未观察到Al3+与全铁转铁蛋白有相互作用，这表明在所采用的实验条件下Al3+无法取代Fe3+。Al3+与脱铁转铁蛋白相互作用后，在280或295nm激发下观察到色氨酸荧光增强（最大波长在330nm）。与Al3+相互作用后，脱铁转铁蛋白荧光带的波长没有变化，但强度确实增加了。由于在295nm激发对色氨酸残基具有特异性，因此必定是色氨酸而非酪氨酸导致了荧光强度的变化。荧光减弱是Fe3+与脱铁转铁蛋白结合的结果。Al3+结合对脱铁转铁蛋白的远紫外CD光谱有轻微影响，但在酪氨酸和色氨酸吸收的近紫外约288nm处观察到显著变化。得出的结论是，Al3+与脱铁转铁蛋白结合诱导了蛋白质发生微小的构象变化。
