ID 4 GLUTAMYL RADICAL AS INTERMEDIATE IN CARBON SKELETON REARRANGEMENT

使用一系列2 H和13 C标记的谷氨酸盐作为底物 对于辅酶B12依赖性谷氨酸盐， （S）-谷氨酸与（2S，3S）-3-甲基谷氨酸。 这些化合物 在碳链的C-2、C-3或C-4上含有同位素： [2- 2 H]、[3- 2 H2]、[4- 2 H2]、[2，3，3，4，4 - 2 H5]、[2- 13 C]、[3- 13 C]和 [4- 13 C]谷氨酸。 通过EPR光谱监测每个反应， 显示出类似的信号，其特征在于g ′ xy = 2.1，g ′ z =1.985， A'=5.0mT。 光谱数据的解释得到了以下方面的帮助： 模拟结果与实验结果非常吻合。 这种方法 支持了形成激进对的想法，包括 cob（II）alamin与有机自由基相互作用，距离为 6.6+/- 0.9A。 观察到的超精细耦合与 未标记的谷氨酸与标记的谷氨酸之间的相互作用， 主要贡献者的自由基对被确定为 4-glytamyl自由基 这些发现支持了目前公认的 谷氨酸还原反应的机理，即该过程是 通过从谷氨酸的C-4中提取氢原子引发， 5 '-脱氧腺苷自由基，它是由同型分解的 辅酶B21的Co-C σ键。

A series of 2H- and 13C-labeled glutamates were used as substrates for coenzyme B12-dependent glutamate mutase, which equilibrates (S)-glutamate with (2S, 3S)-3-methylasparate. These compounds contained the isotopes at C-2, C-3 or C-4 of the carbon chain: [2-2H], [3-2H2], [4-2H2], [2,3,3,4,4-2H5], [2-13C], [3-13C], and [4-13C]glutamate. Each reaction was monitored by EPR spectroscopy and revealed a similar signal characterized by g'xy=2.1,g'z=1.985 and A'=5.0mT. The interpretation of the spectral data was aided by simulations which gave close agreement with experiment. This approach underpinned the idea of the formation of a radical pair, consisting of cob(II)alamin interacting with an organic radical at a distance of 6.6+/- 0.9A. Comparison of the hyperfine couplings observed with unlabeled glutamate with those from the labeled glutamates enabled a principle contributor to the radical pair to be identiied as the 4-glytamyl radical. These findings support the currently accepted mechanism for the glutamate mutase reaction, i.e. the process is initiated through hydrogen atom abstraction from C-4 of glutamate by the 5'-deoxyadenosyl radical, which is derived by homolysis of the Co-C sigma-bond o the coenzyme B21.