Osumi T, Katsuki H
J Biochem. 1977 Mar;81(3):771-8. doi: 10.1093/oxfordjournals.jbchem.a131515.
When [14C]propionate was incubated with a cell-free extract of Rhodospirillum rubrum in the presence of glyoxylate, ATP, CoA, Mg2+, and Mn2+, radioactivity was incorporated into mesaconate (MSA) as well as into beta-methylmalate (MMA) and citramalate (CMA). MSA was suggested to be an intermediate of the conversion of MMA to CMA based on the following observations. (i) When non-labeled MSA was added to the CMA-forming reaction system, radioactivity was trapped in MSA. (ii) When MSA was incubated with the cell-free extract, CMA was formed. (iii) The alpha-carboxyl group of CMA was shown to be derived from the beta-carboxyl group of MMA, implying that CMA was formed from MMA via MSA through successive dehydration and hydration. From the results of Sephadex G-10 column chromatography of the reaction products, beta-methylmalyl-CoA and mesaconyl-CoA were presumed to be involved in the reaction. A new CMA-forming metabolic pathway is proposed as follows: erythro-beta-methylamalyl-CoA leads to mesaconyl-CoA leads to MSA leads to L-CMA.
当在乙醛酸、ATP、辅酶A、Mg2+和Mn2+存在的情况下，将[14C]丙酸盐与深红红螺菌的无细胞提取物一起温育时，放射性被掺入到中康酸（MSA）以及β-甲基苹果酸（MMA）和柠苹酸（CMA）中。基于以下观察结果，MSA被认为是MMA转化为CMA的中间体。（i）当将未标记的MSA添加到形成CMA的反应体系中时，放射性被困在MSA中。（ii）当将MSA与无细胞提取物一起温育时，形成了CMA。（iii）CMA的α-羧基被证明来源于MMA的β-羧基，这意味着CMA是通过MSA由MMA经连续的脱水和水合作用形成的。从反应产物的葡聚糖G-10柱色谱结果推测，β-甲基苹果酰辅酶A和中康酰辅酶A参与了该反应。提出了一种新的形成CMA的代谢途径如下：赤藓糖型β-甲基苹果酰辅酶A生成中康酰辅酶A生成MSA生成L-CMA。
