Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada.
MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI, USA.
Nat Plants. 2024 Oct;10(10):1453-1463. doi: 10.1038/s41477-024-01791-z. Epub 2024 Oct 4.
RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE/OXYGENASE (Rubisco) produces pyruvate in the chloroplast through β-elimination of the aci-carbanion intermediate. Here we show that this side reaction supplies pyruvate for isoprenoid, fatty acid and branched-chain amino acid biosynthesis in photosynthetically active tissue. C labelling studies of intact Arabidopsis plants demonstrate that the total carbon commitment to pyruvate is too large for phosphoenolpyruvate to serve as a precursor. Low oxygen stimulates Rubisco carboxylase activity and increases pyruvate production and flux through the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway, which supplies the precursors for plastidic isoprenoid biosynthesis. Metabolome analysis of mutants defective in phosphoenolpyruvate or pyruvate import and biochemical characterization of isolated chloroplasts further support Rubisco as the main source of pyruvate in chloroplasts. Seedlings incorporated exogenous,C-labelled pyruvate into MEP pathway intermediates, while adult plants did not, underscoring the developmental transition in pyruvate sourcing. Rubisco β-elimination leading to pyruvate constituted 0.7% of the product profile in in vitro assays, which translates to 2% of the total carbon leaving the Calvin-Benson-Bassham cycle. These insights solve the "pyruvate paradox", improve the fit of metabolic models for central metabolism and connect the MEP pathway directly to carbon assimilation.
核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）通过 aci-碳负离子中间体的β消除反应在叶绿体中产生丙酮酸。在这里，我们表明，这种副反应为光合作用组织中的异戊烯基、脂肪酸和支链氨基酸生物合成提供了丙酮酸。对完整拟南芥植物的 C 标记研究表明，用于丙酮酸的总碳投入对于磷酸烯醇丙酮酸来说太大，不能作为前体。低氧刺激 Rubisco 羧化酶活性并增加丙酮酸的产生和通量通过 2-C-甲基-D-赤藓醇-4-磷酸（MEP）途径，该途径为质体异戊烯基生物合成提供前体。磷酸烯醇丙酮酸或丙酮酸导入缺陷突变体的代谢组学分析以及分离的叶绿体的生化特征进一步支持 Rubisco 是叶绿体中丙酮酸的主要来源。幼苗将外源，C 标记的丙酮酸掺入 MEP 途径中间体，而成年植物则不能，强调了丙酮酸来源的发育转变。Rubisco 的β消除导致丙酮酸在体外测定中占产物谱的 0.7%，相当于离开卡尔文-本森-巴斯汉姆循环的总碳的 2%。这些见解解决了“丙酮酸悖论”，改善了中心代谢物代谢模型的拟合，并将 MEP 途径直接连接到碳同化。
