IRON(II)-SUBSTITUTED METALLOTHIONEIN - EVIDENCE FOR THE EXISTENCE OF IRON THIOLATE CLUSTERS
IRON(II)-SUBSTITUTED METALLOTHIONEIN - EVIDENCE FOR THE EXISTENCE OF IRON THIOLATE CLUSTERS
复制标题
DOI：
10.1021/bi00374a003
复制
发表时间：
1986-12-30
期刊：
影响因子：
2.9
通讯作者：
VASAK, M
中科院分区：
文献类型：
--
作者：
GOOD, M;VASAK, M
金属霉素（MT''s）是独特的低分子量（MR 6000-7000）金属和富含半胱氨酸的蛋白质，其特征在于两个四氢四硫酸四硫酸四硫酸酯簇，其中包含三个和四个金属离子。天然存在的蛋白质通常包含二磁金属离子Zn（II）和/或CD（II）。现在，我们已经成功地通过顺磁性Fe（II）代替了这些离子。兔肝MT-1，其中所有七个金属结合位点被Fe（II）离子占据的所有七个金属结合位点显示了四面体四硫酸四二硫酸四二硫酸四二硫酸盐配位的吸收特征。这是由配体5e .fwdarw的存在记录的。 5T2在近侵蚀区域的过渡为约1850 nm（.epsilon.fe.apprxeq。100m-1 cm-1）和肩部为314 nm的紫外线区域的宽电荷转移吸收。从金属离子与半胱氨酸残基的7到20比率推断出金属硫醇簇结构，并从光谱研究中，将Fe（II）的连续增量纳入了无金属蛋白。因此，至大约4次，形成的复合物的电荷转移吸收和磁性圆形甲状腺（MCD）特征非常类似于desulfovibro gigas降低的Rubredoxin的特征，其中四面体四硫酸盐四硫酸四硫酸盐的fe（ii）共同记录了。但是，在进一步添加Fe（II）离子后，电荷转移吸收带底导致了渐进的红移，直到达到每个分子的七个Fe（II）离子的全金属占用率。在MCD光谱中也表现出来的浴色素移位可以归因于某些末端硫醇酸盐配体的转化，当Fe（ii）的完整补体结合时，可以桥接桥接。人们认为，在4 equiv上方的MCD频段的振幅中，伴随损失被认为是由于通过硫醇桥桥接（II）的交换耦合而引起的。
Metallothioneins (MT''s) are unique low molecular weight (Mr 6000-7000) metal- and cysteine-rich proteins characterized by two tetrahedral tetrathiolate clusters containing three and four metal ions. Naturally occurring proteins usually contain the diamagnetic metal ions Zn(II) and/or Cd(II). We have now succeeded in substituting these ions by paramagnetic Fe(II). Rabbit liver MT-1 in which all seven metal binding sites were occupied by Fe(II) ions displays absorption features typical of tetrahedral tetrathiolate Fe(II) coordination. This is documented by the presence of a ligand field 5E .fwdarw. 5T2 transition in the near-infared region centered at about 1850 nm (.epsilon.Fe .apprxeq. 100 M-1 cm-1) and a broad charge-transfer absorption in the UV region with a shoulder at 314 nm. A metal-thiolate cluster structure is inferred from the 7 to 20 ratio of metal ions to cysteine residues and from spectral studies in which successive increments of Fe(II) were incorporated into the metal-free protein. Thus, to about 4 equiv, the charge-transfer absorption and magnetic circular dichroism (MCD) features of the complexes formed resemble closely those of reduced rubredoxin from Desulfovibro gigas in which tetrahedral tetrathiolate Fe(II) coordination is documented. However, upon further addition of Fe(II) ions, the charge-transfer absorption bands undero a progressive red-shift until the full metal occupancy of seven Fe(II) ions per molecule is reached. The bathochromic shift which is also manifested in the MCD spectra can be ascribed on the transformation of some of the terminal thiolate ligands to bridging when the full complement of Fe(II) is bound. The concomitant loss in amplitude of the MCD bands above 4 equiv is thought to arise from exchange coupling of vicinal Fe(II) via the thiolate bridges.