Rauser W E, Meuwly P
Department of Botany, University of Guelph, Ontario, Canada.
Plant Physiol. 1995 Sep;109(1):195-202. doi: 10.1104/pp.109.1.195.
Cd from roots of maize was partitioned in seedlings exposed to 3 microM CdSO4 for 1 to 7 d. Most of the root Cd (92-94%) was buffer soluble and provided the classical metal-induced cysteine-rich, high-molecular-weight Cd-binding complex. This complex, however, bound only part of the Cd within the roots, from 19% after 1 d of exposure to 59% by d 7. Three families of peptides formed the Cd-binding complex: (gamma-glutamic acid-cysteine)n-glycine [(gamma-Glu-Cys)n-Gly], or phytochelatins, (gamma-Glu-Cys)n, and (gamma-Glu-Cys)n-Glu. The monothiols gamma-Glu-Cys-Gly (glutathione), gamma-Glu-Cys, and gamma-Glu-Cys-Glu were absent from the complex. The n2 oligomers of any peptide were the least concentrated, whereas the n3 and n4 oligomers increased in the complex with exposure to Cd. By d 7, 75% of (gamma-Glu-Cys)4-Gly, 80% of (gamma-Glu-Cys)4, and 73% of (gamma-Glu-Cys)3-Glu were complexed with Cd. The peptide thiol:Cd molar ratio for the complexes was 1.01 +/- 0.07, as if the minimal amount of thiol was used to bind Cd. Acid-labile sulfide occurred in the complexes from d 1 onward at the low S2-;Cd molar ratio of 0.18 +/- 0.02.
将暴露于3 microM硫酸镉1至7天的玉米幼苗根系中的镉进行分配。大部分根系镉（92 - 94%）是缓冲可溶的，并形成了经典的金属诱导的富含半胱氨酸的高分子量镉结合复合物。然而，这种复合物仅结合了根系内部分镉，从暴露1天后的19%增加到第7天的59%。三类肽形成了镉结合复合物：（γ-谷氨酰-半胱氨酸）n-甘氨酸[（γ-Glu-Cys）n-Gly]，即植物螯合肽，（γ-Glu-Cys）n，以及（γ-Glu-Cys）n-Glu。复合物中不存在单硫醇γ-Glu-Cys-Gly（谷胱甘肽）、γ-Glu-Cys和γ-Glu-Cys-Glu。任何肽的n2低聚物浓度最低，而n3和n4低聚物在暴露于镉时在复合物中增加。到第7天，75%的（γ-Glu-Cys）4-Gly、80%的（γ-Glu-Cys）4和73%的（γ-Glu-Cys）3-Glu与镉络合。复合物的肽硫醇：镉摩尔比为1.01±0.07，就好像用了最少的硫醇来结合镉。从第1天起，复合物中就出现了酸不稳定硫化物，其S2-；镉摩尔比为0.18±0.02。
