Glutathione and other intracellular low molecular mass thiols act both as the major endogenous antioxidant and redox buffer system and, as recently highlighted, as an important regulator of cellular homeostasis. Such cellular functions are mediated by protein thiolation, a newly recognized post-translational modification which involves the formation of mixed disulfides between GSH and key disulfide-linked Cys residues in the native protein structure. It is also well known that thiol-seeking heavy metals, such as mercury, cadmium and lead, may interfere in this regulatory system, thus disrupting the cellular functioning. To identify such mixed disulfides in order to investigate their biological role, 15 homo- and heterodimeric disulfides were prepared by air oxidation of binary mixtures containing cysteine, homocysteine, penicillamine, N-acetylcysteine, N-acetylpenicillamine and glutathione and their protonated molecules were characterized by mass spectrometry. Collisionally activated unimolecular decomposition of protonated homo- and heterodimeric disulfides generated by electrospray ionization gives rise to fission of the disulfide system both between the two sulfur atoms and across the CS bonds, to yield structurally specific fragments which allow one to define the structure of the compounds and to discriminate between isomeric compounds. Fission between the sulfur atoms yields a pair of RS+ ions and, in some cases, also the complementary fragments corresponding to the protonated amino acids. Fission across the CS bonds mainly occurs in the disulfides of N-acetylcysteine and N-acetylpenicillamine and gives rise to non-S-containing fragments formally similar to those obtained from some mercapturic acids. The complementary fragments, formally connected as RSS+ ions are also observed. Fragmentation of glutathione disulfides mainly shows the characteristic loss of the terminal γ-linked glutamic acid and little, if any, fragmentation of the disulfide system. Copyright © 2004 John Wiley & Sons, Ltd.
谷胱甘肽和其他细胞内低分子量
硫醇既是主要的内源性
抗氧化剂和
氧化还原缓冲系统,也正如最近强调的那样,是细胞稳态的重要调节因子。这种细胞功能的介导依赖于蛋白质
硫化,这是一种新识别的翻译后修饰,涉及
谷胱甘肽与本征蛋白结构中关键的二
硫键连接的半胱
氨酸残基之间形成混合二
硫化物。众所周知,寻
硫重
金属如
汞、
镉和
铅可能干扰这一调节系统,从而破坏细胞功能。为了鉴定这些混合二
硫化物以探讨它们的
生物学作用,通过空气
氧化含有半胱
氨酸、同型半胱
氨酸、
青霉胺、
N-乙酰半胱
氨酸、
N-乙酰青霉胺和
谷胱甘肽的二元混合物,制备了15种同二聚体和异二聚体二
硫化物,并通过质谱对其质子化分子进行了表征。通过电喷雾电离生成的质子化同二聚体和异二聚体二
硫化物发生碰撞激活的单分子解离,引发二
硫化物系统在两个
硫原子之间及CS键上的裂解,产生结构特异的片段,这些片段可以用来确定化合物的结构并区分异构化合物。
硫原子之间的裂解产生一对RS+离子,在某些情况下,还会产生与质子化
氨基酸对应的互补片段。CS键的裂解主要发生在
N-乙酰半胱
氨酸和
N-乙酰青霉胺的二
硫化物中,并产生在形式上类似于一些巯基酸获得的非S含 Fragment。互补片段在形式上连接为RSS+离子也被观察到。
谷胱甘肽二
硫化物的裂解主要显示终端γ-连接的谷
氨酸的特征性损失,几乎没有或很少有二
硫化物系统的裂解。版权 © 2004 John Wiley & Sons, Ltd.