Meuwly P, Thibault P, Schwan A L, Rauser W E
Department of Botany, University of Guelph, Ont., Canada.
Plant J. 1995 Mar;7(3):391-400. doi: 10.1046/j.1365-313x.1995.7030391.x.
Phytochelatins ((gamma GluCys)nGly) are synthesized from glutathione by plants exposed to metals like Cd2+, Cu2+ and Zn2+. An intracellular complex formed by phytochelatins with Cd2+ and sulfide is thought to detoxify the metal possibly by sequestration in the vacuole. It was found that maize seedlings exposed to Cd2+ produced phytochelatins and two additional families of cysteine-containing peptides, (gamma GluCys)n and (gamma GluCys)nGlu. All thiol peptides with n = 2 and 3 were purified and their structure characterized by tandem mass spectrometry. For maize plants exposed to Cd2+ for 7 days, phytochelatins were synthesized preferentially in the first 24 h whereas the amounts of (gamma GluCys)n and (gamma GluCys)nGlu were the highest thereafter. This was probably due to an initial large pool of glutathione available in control plants compared with a dearth of gamma GluCys and no detectable gamma GluCysGlu. The (gamma GluCys)nGlu peptides were induced exclusively by Cd2+ as they were below the detection limit in control seedlings that contained low amounts of phytochelatins and (gamma GluCys)n. Since the Cys moiety of the peptides is essential for binding Cd2+, a role for accumulated (gamma GluCys)n and (gamma GluCys)nGlu in detoxifying Cd2+ in plants must be considered.
植物螯合肽（(γ-谷氨酰半胱氨酸)n甘氨酸）由暴露于镉离子、铜离子和锌离子等金属的植物从谷胱甘肽合成。植物螯合肽与镉离子和硫化物形成的细胞内复合物被认为可能通过在液泡中隔离来使金属解毒。研究发现，暴露于镉离子的玉米幼苗产生了植物螯合肽以及另外两个含半胱氨酸的肽家族，即(γ-谷氨酰半胱氨酸)n和(γ-谷氨酰半胱氨酸)n谷氨酸。所有n = 2和3的硫醇肽均被纯化，并通过串联质谱对其结构进行了表征。对于暴露于镉离子7天的玉米植株，植物螯合肽在前24小时优先合成，而(γ-谷氨酰半胱氨酸)n和(γ-谷氨酰半胱氨酸)n谷氨酸的含量此后最高。这可能是由于与缺乏γ-谷氨酰半胱氨酸且未检测到γ-谷氨酰半胱氨酸谷氨酸的对照植株相比，对照植株中最初有大量的谷胱甘肽储备。(γ-谷氨酰半胱氨酸)n谷氨酸肽仅由镉离子诱导产生，因为它们在含有少量植物螯合肽和(γ-谷氨酰半胱氨酸)n的对照幼苗中低于检测限。由于肽的半胱氨酸部分对于结合镉离子至关重要，因此必须考虑积累的(γ-谷氨酰半胱氨酸)n和(γ-谷氨酰半胱氨酸)n谷氨酸在植物镉离子解毒中的作用。
