Reese R N, Wagner G J
Biochem J. 1987 Feb 1;241(3):641-7. doi: 10.1042/bj2410641.
The chemical and physical characteristics of Cd-binding peptides isolated from tobacco (Nicotiana tabacum) leaves and suspension-cultured tobacco cells were determined and compared with properties of rat liver Cd,Zn-thionein. Some emphasis was placed on metal-binding and specificity properties. Cd-peptides of apparent Mr 6000 and 2000 were induced in tobacco leaves by growth of plants with 90 microM-Cd. Only the apparent-Mr-2000 Cd-peptide was induced in the leaves of tobacco plants grown in the presence of 3 microM-Cd. In cultured tobacco cells exposed to a wide range of Cd levels (3-180 microM), a peptide of apparent Mr 2000 was observed. Under denaturing conditions [6 M-guanidinium chloride (GdmCl) with or without 100 mM-2-mercaptoethanol], all of the above forms were shown to have an Mr of approx. 1300, compared with an Mr of 6000 for Cd,Zn-thionein. The apparent disaggregation of the Mr-6000 form by GdmCl to what appears to be the unit Cd-binding peptide was reversible. Tobacco-derived Cd-peptide contained approx. 40, 35 and 15 residues of glutamate/glutamine, cysteine and glycine respectively, with serine, lysine, and aromatic residues being absent. Tobacco Cd-peptide had an isoelectric point (pI) of 3.15, which is lower than the pI greater than or equal to 4 reported for metallothionein. A 50% dissociation of Cd occurred at pH 5 and 3.5 for the tobacco Cd-peptide and Cd,Zn-thionein respectively, and GdmCl was shown to cause Cd dissociation from tobacco peptide, but not from metallothionein. No evidence was obtained for Zn induction in vivo of, or Zn binding in vitro to, tobacco Cd-peptide. Copper induced a low-Mr metal-binding component in cultured tobacco cells which did not appear to be identical with the peptide induced by Cd. Properties of tobacco Cd-peptide and Cd,Zn-thionein, including metal affinity and selectivity, are greatly different, except for the common presence of 30 residues of cysteine/100 residues.
对从烟草（Nicotiana tabacum）叶片和悬浮培养的烟草细胞中分离出的镉结合肽的化学和物理特性进行了测定，并与大鼠肝脏镉、锌硫蛋白的特性进行了比较。重点研究了金属结合和特异性特性。通过在含有90微摩尔镉的条件下培养植物，在烟草叶片中诱导出了表观分子量为6000和2000的镉肽。在含有3微摩尔镉的条件下生长的烟草植株叶片中，只诱导出了表观分子量为2000的镉肽。在暴露于广泛镉水平（3 - 180微摩尔）的培养烟草细胞中，观察到一种表观分子量为2000的肽。在变性条件下[6摩尔/升氯化胍（GdmCl），有或没有100毫摩尔2 - 巯基乙醇]，上述所有形式的表观分子量均显示约为1300，而镉、锌硫蛋白的表观分子量为6000。GdmCl使表观分子量为6000的形式明显解聚为似乎是单位镉结合肽的过程是可逆的。烟草来源的镉肽分别含有约40、35和15个谷氨酸/谷氨酰胺、半胱氨酸和甘氨酸残基，不存在丝氨酸、赖氨酸和芳香族残基。烟草镉肽的等电点（pI）为3.15，低于报道的金属硫蛋白的pI（大于或等于4）。烟草镉肽和镉、锌硫蛋白的镉分别在pH 5和3.5时发生50%的解离，并且GdmCl被证明会导致镉从烟草肽中解离，但不会从金属硫蛋白中解离。没有获得体内锌诱导或体外锌结合到烟草镉肽的证据。铜在培养烟草细胞中诱导出一种低分子量的金属结合成分，它似乎与镉诱导的肽不同。除了都含有30个半胱氨酸残基/100个残基外，烟草镉肽和镉、锌硫蛋白的特性，包括金属亲和力和选择性，有很大差异。
