Reese R N, Winge D R
Department of Medicine, University of Utah Medical Center, Salt Lake City 84132.
J Biol Chem. 1988 Sep 15;263(26):12832-5.
Addition of cadmium salts to the growth medium of Schizosaccharomyces pombe leads to synthesis of a Cd.gamma-Glu peptide complex and an enhanced generation of sulfide ions. The gamma-Glu peptide complex functions in the detoxification of heavy metal ions. Native Cd.gamma-Glu peptide complexes contain acid-labile sulfide in the metal-thiolate cluster. Two forms of the complex exist differing primarily in their sulfide content. Sulfide concentrations up to 0.2 and 1.2 mol/mol of peptide were observed in native isolates of forms I and II, respectively. Addition of sulfide to the low sulfide form I converted it to a complex similar to form II. Properties of the Cd.gamma-Glu peptide complex were altered by the incorporation of sulfide ions. Sulfide-dependent electronic transitions in the ultraviolet were evident, and the absorbance maximum of the transition was related to the sulfide content and the bound metal ion. High sulfide forms of the Cd and Zn complexes exhibited absorbance peaks at 318 nm and 255 nm, respectively. Incorporation of sulfide into the Cd.gamma-Glu peptide complex imparted greater thermodynamic stability to the complex, an increased Stokes radius, and an enhanced Cd(II) binding capacity. Sulfide generation may be a cellular response in part to enhance the effectiveness of the gamma-Glu peptide system for Cd(II) detoxification.
向粟酒裂殖酵母的生长培养基中添加镉盐会导致合成一种镉-γ-谷氨酰胺肽复合物，并增强硫离子的生成。γ-谷氨酰胺肽复合物在重金属离子解毒中发挥作用。天然的镉-γ-谷氨酰胺肽复合物在金属硫醇盐簇中含有酸不稳定的硫化物。该复合物存在两种形式，主要区别在于它们的硫化物含量。在形式I和II的天然分离物中，分别观察到高达0.2和1.2摩尔/摩尔肽的硫化物浓度。向低硫化物形式I中添加硫化物会将其转化为类似于形式II的复合物。镉-γ-谷氨酰胺肽复合物的性质因硫化物离子的掺入而改变。在紫外线下明显存在依赖于硫化物的电子跃迁，跃迁的最大吸光度与硫化物含量和结合的金属离子有关。镉和锌复合物的高硫化物形式分别在318纳米和255纳米处表现出吸收峰。将硫化物掺入镉-γ-谷氨酰胺肽复合物中赋予该复合物更大的热力学稳定性、增加的斯托克斯半径和增强的镉（II）结合能力。硫化物的生成可能部分是一种细胞反应，以增强γ-谷氨酰胺肽系统对镉（II）解毒的有效性。
