Choong Y S, Massey V
Eur J Biochem. 1983 Apr 5;131(3):501-8. doi: 10.1111/j.1432-1033.1983.tb07290.x.
The natural flavin of lactate oxidase, FMN, was removed and replaced by the synthetic flavin 2-thioriboflavin 5'-phosphate (2-thio FMN). Despite the difference in properties of the flavins, including an oxidation-reduction potential some 80 mV more positive than that of normal flavin the 2-thio-FMN enzyme behaves in practically all respects like the native enzyme. It catalyzes the oxidative decarboxylation of L-lactate with almost the same efficiency as the native enzyme and with similar kinetic constants for individual steps in the catalytic pathway. It forms covalent derivatives at the flavin N(5) and C(4a) positions in facile photochemical reactions analogous to those of the native enzyme. It also forms a flavin anion radical on photoreduction with 5-deazaflavin as catalyst and, as with the native enzyme, this radical is stabilized remarkably on formation of a complex with pyruvate. The spectral properties of the neutral flavin radical form of 2-thioflavin are also reported, as determined by photochemical reduction of 2-thio-FMN flavodoxin. Like native lactate oxidase, the 2-thio-FMN enzyme also forms a flavin N(5)-sulfite adduct in an equilibrium reaction with sulfite. These results demonstrate clearly with this enzyme that the native flavin may be removed and replaced by an artificial flavin, without altering the structural integrity of the protein.
乳酸氧化酶的天然黄素FMN被去除，代之以合成黄素2-硫代核黄素5'-磷酸（2-硫代FMN）。尽管这两种黄素的性质存在差异，包括氧化还原电位比正常黄素约正80 mV，但2-硫代FMN酶在几乎所有方面的表现都与天然酶相似。它催化L-乳酸的氧化脱羧反应，效率几乎与天然酶相同，催化途径中各个步骤的动力学常数也相似。它在类似于天然酶的光化学反应中，在黄素的N(5)和C(4a)位置形成共价衍生物。它在以5-脱氮黄素为催化剂的光还原过程中也形成黄素阴离子自由基，并且与天然酶一样，该自由基在与丙酮酸形成复合物时能显著稳定。还报道了通过2-硫代-FMN黄素氧还蛋白的光化学还原测定的2-硫代黄素中性黄素自由基形式的光谱特性。与天然乳酸氧化酶一样，2-硫代-FMN酶在与亚硫酸盐的平衡反应中也形成黄素N(5)-亚硫酸盐加合物。这些结果清楚地表明，对于这种酶而言，天然黄素可以被人工黄素取代，而不会改变蛋白质的结构完整性。
