菠菜叶片乙醇酸氧化酶的氧化甘油酸活性

首先从菠菜叶片中纯化了乙醇酸氧化酶（GO）。通过鉴定反应中氧的消耗以及反应产物H2O2的生成，证实菠菜GO具有氧化光呼吸途径中间代谢物甘油酸的活性。该氧化活性依赖于辅因子FMN和FAD，而不依赖核黄素和光黄素；其最适反应pH值为8．0，Km（甘油酸）值为7．14mmol／L，kcat值为1．04s^-1，活化能为17．29kJ／mol；草酸和丙酮酸对该氧化活性有明显的抑制作用，其中前者为典型的竞争性抑制。进一步通过两底物竞争作图表明：菠菜叶片GO氧化甘油酸反应和氧化乙醇酸反应为同一活性中心所催化。

Glycerate-oxidizing Activity of Glycolate Oxidase from Leaves of Spinacia oleracea

Glycolate oxidase (GO) was purified to ho-mogeneity from leaves of spinach (Spinacia oleracea).Through detecting the consumption of oxygen and theformation of hydrogen peroxide in the assay solution, itwas found that GO could also oxidize glycerate, anothermetabolite in the photorespiratory pathway, and use FMNand FAD, but not riboflavin and lumiflavin, as itscofactors. The optimum reaction pH, Km for glycerate,kcat and activation energy of this oxidizing reaction weredetermined to be 8.0, 7.14 mmol/L, 1.04 s-1 and 17.29kJ/mol, respectively. Oxalate and pyruvate at 5.0 mmol/L could inhibit the glycerate-oxidizing activity by 34%and 26%, and oxalate acted as a competitive inhibitor ofthe glycerate oxidation reaction with a Ki of 0.75 mmol/L. By the competition plotting with mixed-substrates, itwas indicated that glycolate-oxidizing activity andglycerate-oxidizing activity of GO shared the same ac-tive site.