The role of pyruvate ferredoxin oxidoreductase in pyruvate synthesis during autotrophic growth by the Wood-Ljungdahl pathway
The role of pyruvate ferredoxin oxidoreductase in pyruvate synthesis during autotrophic growth by the Wood-Ljungdahl pathway
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DOI：
10.1074/jbc.m003291200
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发表时间：
2000-09-15
影响因子：
4.8
通讯作者：
Ragsdale, SW
中科院分区：
文献类型：
--
作者：
Furdui, C;Ragsdale, SW
丙酮酸：铁氧还蛋白氧化还原酶(PFOR)催化丙酮酸氧化脱羧制乙酰辅酶A和二氧化碳。对于丙酮酸合酶这种逆转反应的催化能力，人们知之甚少。乙酰辅酶A向丙酮酸的转化将自养CO2固定的Wood-Ljugdahl途径与还原三羧酸循环联系起来，在这些自养厌氧菌中，三羧酸循环是所有细胞大分子生物合成的阶段。这些结果表明，热醋酸梭菌PFOR是一种高效的丙酮酸合成酶。催化合成丙酮酸的米氏参数为：V-max=1.6U/mg(k(CAT)=3.2 S(-1))，K-m(乙酰辅酶A)=9muM，K-m(CO_2)=2 mm。测量了细胞内乙酰辅酶A、辅酶A和丙酮酸的浓度。在生理底物浓度下预测的丙酮酸合成速率显然足以支持PFOR在体内作为丙酮酸合成酶的作用。对其k(CAT)/K-m值的测定表明，铁氧还蛋白在氧化和还原反应中都是一种高效的电子载体。另一方面，Rubredoxin在氧化方向上是一个很差的替代品，不能为丙酮酸的合成提供电子。
Pyruvate:ferredoxin oxidoreductase (PFOR) catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA and CO2. The catalytic proficiency of this enzyme for the reverse reaction, pyruvate synthase, is poorly understood. Conversion of acetyl-CoA to pyruvate links the Wood-Ljungdahl pathway of autotrophic CO2 fixation to the reductive tricarboxylic acid cycle, which in these autotrophic anaerobes is the stage for biosynthesis of all cellular macromolecules. The results described here demonstrate that the Clostridium thermoaceticum PFOR is a highly efficient pyruvate synthase. The Michaelis-Menten parameters for pyruvate synthesis by PFOR are: V-max = 1.6 unit/mg (k(cat) = 3.2 s(-1)), K-m(Acetyl-CoA) = 9 mu M, and K-m(CO2) = 2 mM. The intracellular concentrations of acetyl-CoA, CoASH, and pyruvate have been measured. The predicted rate of pyruvate synthesis at physiological concentrations of substrates clearly is sufficient to support the role of PFOR as a pyruvate synthase in vivo. Measurements of its k(cat)/K-m values demonstrate that ferredoxin is a highly efficient electron carrier in both the oxidative and reductive reactions. On the other hand, rubredoxin is a poor substitute in the oxidative direction and is inept in donating electrons for pyruvate synthesis.