Stillman M J, Szymanska J A
Department of Chemistry, University of Western Ontario, London, Ontario N6A 5B7, Canada.
Biophys Chem. 1984 Mar;19(2):163-9. doi: 10.1016/0301-4622(84)85016-4.
Absorption, circular dichroism (CD), magnetic circular dichroism (MCD) and emission spectra of rat liver and rat kidney cadmium-, zinc- and copper-containing metallothioneins (MT) are reported. The absorption, CD and MCD data of native rat kidney Cd,Cu-MT protein closely resemble data recorded for the rat liver Cd,Zn-MT. This suggests that the major features in all three spectra of the native Cd,Cu-MT are dominated by cadmium-related bands. The CD spectrum of the Cd,Cu-MT recorded at pH 2.7 has the same band envelope that is observed for a Cd,Cu-MT formed in vitro by titration of Cd,Zn-MT with Cu(I), suggesting that the copper occupies the zinc sites in Cd,Cu-MT formed both in vivo and, at low molar ratios, in vitro. Remetallalion of the metallothionein from low pH in the presence of both copper and cadmium results in considerably less cadmium bound to the protein than was present in the native sample. It is suggested that this is due to the effect of the distribution of the copper amongst all available binding sites, thus inhibiting cluster formation by the cadmium. Emission spectra are reported for the first time for a cadmium- and copper-containing metallothionein. An emission band at 610 nm is shown to be a sensitive indicator of Cu(I) binding to metallothionein. Both the native Cd,Cu-MT and a Cd,Cu-MT formed in vitro exhibit an excitation spectrum with a band in the copper-thiolate charge-transfer region.
报道了大鼠肝脏和大鼠肾脏中含镉、锌和铜的金属硫蛋白（MT）的吸收光谱、圆二色性（CD）、磁圆二色性（MCD）和发射光谱。天然大鼠肾脏镉、铜 - MT蛋白的吸收、CD和MCD数据与大鼠肝脏镉、锌 - MT记录的数据非常相似。这表明天然镉、铜 - MT的所有三种光谱中的主要特征都由镉相关的谱带主导。在pH 2.7下记录的镉、铜 - MT的CD光谱具有与通过用Cu（I）滴定镉、锌 - MT在体外形成的镉、铜 - MT观察到的相同的谱带包络，这表明铜占据了体内形成的以及在低摩尔比下体外形成的镉、铜 - MT中的锌位点。在铜和镉存在的情况下，金属硫蛋白从低pH值进行再金属化导致与蛋白质结合的镉比天然样品中的少得多。有人认为这是由于铜在所有可用结合位点之间分布的影响，从而抑制了镉的簇形成。首次报道了含镉和铜的金属硫蛋白的发射光谱。610nm处的发射带被证明是Cu（I）与金属硫蛋白结合的敏感指标。天然镉、铜 - MT和体外形成的镉、铜 - MT都表现出在硫醇铜电荷转移区域有一个谱带的激发光谱。
