Kretchmar S A, Teixeira M, Huynh B H, Raymond K N
Department of Chemistry, University of California, Berkeley 94720.
Biol Met. 1988;1(1):26-32. doi: 10.1007/BF01128014.
Electrophoretically purified 57Fe-enriched monoferric and diferric human transferrins and selectively labeled complexes ([C-56Fe,N-57Fe]transferrin and [C-57Fe,N-56Fe]transferrin) were studied by Mössbauer spectroscopy. The data were recorded at 4.2 K over a wide range of applied magnetic fields (0.05-6 T) and were analyzed by a spin-Hamiltonian formalism. Characteristic hyperfine parameters were found and the obtained zero-field splitting parameters (D = 0.25 +/- 0.05 cm-1 and E/D = 0.30 +/- 0.02) agree with previous electron paramagnetic resonance (EPR) findings. The weak-field spectra of the [N-57Fe]transferrin are slightly broader than those of the [C-57Fe]transferrin, indicating that the N-terminal iron site may be more heterogeneous. However, the absorption line positions and the relative intensities of the subspectra originating from the three Kramers doublets of each Fe3+ site are identical. Thus the electronic structures of the two iron sites can be described by the same set of spin-Hamiltonian parameters, indicating that the ligand environments for the two sites are the same, as suggested by the recent X-ray crystallographic studies. This suggestion is further supported by the observation that the strong-field spectra of the two monoferric transferrins are indistinguishable. The selectively labeled mixed-isotope transferrins exhibit spectra that are identical to those of the corresponding monoferric 57Fe-enriched transferrins, implying that the occupation of one iron site has little or no effect on the immediate environment of the other site, a finding that is not surprising since the two sites are separated by approximately 4.2 nm.
通过穆斯堡尔谱对电泳纯化的富含57Fe的单铁和双铁人转铁蛋白以及选择性标记的配合物（[C-56Fe,N-57Fe]转铁蛋白和[C-57Fe,N-56Fe]转铁蛋白）进行了研究。数据在4.2 K下于很宽的外加磁场范围（0.05 - 6 T）内记录，并通过自旋哈密顿形式进行分析。发现了特征超精细参数，所得到的零场分裂参数（D = 0.25 ± 0.05 cm-1，E/D = 0.30 ± 0.02）与先前的电子顺磁共振（EPR）结果一致。[N-57Fe]转铁蛋白的弱场谱比[C-57Fe]转铁蛋白的略宽，表明N端铁位点可能更具异质性。然而，源自每个Fe3+位点的三个克莱默斯双重态的吸收线位置和子谱的相对强度是相同的。因此，两个铁位点的电子结构可以用同一组自旋哈密顿参数来描述，这表明如最近的X射线晶体学研究所暗示的，两个位点的配体环境是相同的。这一推测进一步得到以下观察结果的支持：两种单铁转铁蛋白的强场谱无法区分。选择性标记的混合同位素转铁蛋白所呈现的谱与相应的富含57Fe的单铁转铁蛋白的谱相同，这意味着一个铁位点的占据对另一个位点的紧邻环境几乎没有影响，鉴于两个位点相隔约4.2 nm，这一发现并不令人惊讶。
