Furdui C, Ragsdale S W
Department of Biochemistry, Beadle Center, University of Nebraska, Lincoln, Nebraska 68588-0664, USA.
J Biol Chem. 2000 Sep 15;275(37):28494-9. doi: 10.1074/jbc.M003291200.
Pyruvate:ferredoxin oxidoreductase (PFOR) catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA and CO(2). 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 CO(2) 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 micrometer, and K(m)(CO(2)) = 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.
铁氧化还原蛋白氧化还原酶（PFOR）催化丙酮酸氧化脱羧生成乙酰辅酶A和二氧化碳。人们对该酶催化丙酮酸合酶的逆反应的催化效率了解甚少。乙酰辅酶A转化为丙酮酸将自养二氧化碳固定的伍德-Ljungdahl途径与还原性三羧酸循环联系起来，在这些自养厌氧菌中，还原性三羧酸循环是所有细胞大分子生物合成的阶段。此处描述的结果表明，嗜热栖热菌PFOR是一种高效的丙酮酸合酶。PFOR催化丙酮酸合成的米氏参数为：V(max)=1.6单位/毫克（k(cat)=3.2秒^(-1)），K(m)(乙酰辅酶A)=9微摩尔，K(m)(二氧化碳)=2毫摩尔。已测量了乙酰辅酶A、辅酶A和丙酮酸的细胞内浓度。在底物生理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酶的作用。对其k(cat)/K(m)值的测量表明，铁氧化还原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，红素氧还蛋白在氧化方向上是一种较差的替代物，并且不能为丙酮酸合成提供电子。
