Relative Contributions of Cystathionine β-Synthase and γ-Cystathionase to H2S Biogenesis via Alternative Trans-sulfuration Reactions
Relative Contributions of Cystathionine β-Synthase and γ-Cystathionase to H2S Biogenesis via Alternative Trans-sulfuration Reactions
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DOI：
10.1074/jbc.m109.010868
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发表时间：
2009-08-14
影响因子：
4.8
通讯作者：
Banerjee, Ruma
中科院分区：
文献类型：
--
作者：
Singh, Sangita;Padovani, Dominique;Banerjee, Ruma
在哺乳动物中，硫转移途径中的两种酶，胱硫醚β-合成酶（CBS）和胱硫醚γ-裂解酶（CSE），被认为是硫化氢（H2S）生物合成的主要原因。在这项研究中，我们报告了一个详细的动力学分析的人和酵母CBS催化的反应，导致H2S的产生。来自两种生物体的CBS显示出通过高半胱氨酸β-取代半胱氨酸产生H2S的显著偏好。替代的H2S生成反应，即半胱氨酸的β-消除生成丝氨酸或2 mol半胱氨酸的缩合生成羊毛硫氨酸，在数量上不太显著。动力学数据被用来模拟在生理相关的底物浓度的各种CBS催化的反应的营业额。在等摩尔浓度的CBS和CSE下，模拟预测CBS产生的H2S将占通过转硫途径产生的总H2S的25-70%，这取决于S-腺苷甲硫氨酸对CBS的变构活化的程度。CBS对H2S生成的相对贡献预计在高同型半胱氨酸血症条件下降低。预计CBS实际上是羊毛硫氨酸的唯一来源，并且CSE而不是CBS有效地切割羊毛硫氨酸。CBS催化的H2S生成反应对高同型半胱氨酸血症的不敏感性与CSE的反应性形成鲜明对比，表明CSE在细胞内同型半胱氨酸管理中的作用以前未被认识。最后，我们的研究表明，trans-sulfation途径的挥霍的结果不仅在一个H2S产生的反应的多样性，但也产生新的硫醚代谢物，从而增加了硫代谢组的复杂性。
In mammals, the two enzymes in the trans-sulfuration pathway, cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CSE), are believed to be chiefly responsible for hydrogen sulfide (H2S) biogenesis. In this study, we report a detailed kinetic analysis of the human and yeast CBS-catalyzed reactions that result in H2S generation. CBS from both organisms shows a marked preference for H2S generation by beta-replacement of cysteine by homocysteine. The alternative H2S-generating reactions, i.e. beta-elimination of cysteine to generate serine or condensation of 2 mol of cysteine to generate lanthionine, are quantitatively less significant. The kinetic data were employed to simulate the turnover numbers of the various CBS-catalyzed reactions at physiologically relevant substrate concentrations. At equimolar concentrations of CBS and CSE, the simulations predict that H2S production by CBS would account for similar to 25-70% of the total H2S generated via the trans-sulfuration pathway depending on the extent of allosteric activation of CBS by S-adenosylmethionine. The relative contribution of CBS to H2S genesis is expected to decrease under hyperhomocysteinemic conditions. CBS is predicted to be virtually the sole source of lanthionine, and CSE, but not CBS, efficiently cleaves lanthionine. The insensitivity of the CBS-catalyzed H2S-generating reactions to the grade of hyperhomocysteinemia is in stark contrast to the responsiveness of CSE and suggests a previously unrecognized role for CSE in intracellular homocysteine management. Finally, our studies reveal that the profligacy of the trans-sulfuration pathway results not only in a multiplicity of H2S-yielding reactions but also yields novel thioether metabolites, thus increasing the complexity of the sulfur metabolome.