Rubisco activity is highly regulated and frequently limits carbon assimilation in crop plants. In the chloroplast, various metabolites can inhibit or modulate Rubisco activity by binding to its catalytic or allosteric sites, but this regulation is complex and still poorly understood. Using rice Rubisco, we characterised the impact of various chloroplast metabolites which could interact with Rubisco and modulate its activity, including photorespiratory intermediates, carbohydrates, amino acids; as well as specific sugar-phosphates known to inhibit Rubisco activity - CABP (2-carboxy-d-arabinitol 1,5-bisphosphate) and CA1P (2-carboxy-d-arabinitol 1-phosphate) through in vitro enzymatic assays and molecular docking analysis. Most metabolites did not directly affect Rubisco in vitro activity under both saturating and limiting concentrations of Rubisco substrates, CO2 and RuBP (ribulose-1,5-bisphosphate). As expected, Rubisco activity was strongly inhibited in the presence of CABP and CA1P. High physiologically relevant concentrations of the carboxylation product 3-PGA (3-phosphoglyceric acid) decreased Rubisco activity by up to 30%. High concentrations of the photosynthetically derived hexose phosphates fructose 6-phosphate (F6P) and glucose 6-phosphate (G6P) slightly reduced Rubisco activity under limiting CO2 and RuBP concentrations. Biochemical measurements of the apparent Vmax and Km for CO2 and RuBP (at atmospheric O2 concentration) and docking interactions analysis suggest that CABP/CA1P and 3-PGA inhibit Rubisco activity by binding tightly and loosely, respectively, to its catalytic sites (i.e. competing with the substrate RuBP). These findings will aid the design and biochemical modelling of new strategies to improve the regulation of Rubisco activity and enhance the efficiency and sustainability of carbon assimilation in rice.

中文翻译：

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通过与叶绿体代谢物相互作用调节 Rubisco 活性。


Rubisco 活性受到严格监管，经常限制农作物的碳同化。在叶绿体中，各种代谢物可以通过与其催化或变构位点结合来抑制或调节 Rubisco 活性，但这种调节很复杂，而且人们仍然知之甚少。使用水稻 Rubisco，我们表征了各种叶绿体代谢物的影响，这些代谢物可以与 Rubisco 相互作用并调节其活性，包括光呼吸中间体、碳水化合物、氨基酸；以及通过体外酶测定和分子对接已知抑制 Rubisco 活性的特定糖磷酸酯 - CABP（2-羧基-d-阿拉伯糖醇 1,5-二磷酸）和 CA1P（2-羧基-d-阿拉伯糖醇 1-磷酸）分析。在 Rubisco 底物、CO2 和 RuBP（1,5-二磷酸核酮糖）的饱和浓度和限制浓度下，大多数代谢物不会直接影响 Rubisco 体外活性。正如预期的那样，在 CABP 和 CA1P 存在的情况下，Rubisco 活性受到强烈抑制。高生理相关浓度的羧化产物 3-PGA（3-磷酸甘油酸）可将 Rubisco 活性降低高达 30%。在有限的 CO2 和 RuBP 浓度下，高浓度的光合作用磷酸己糖、果糖 6-磷酸 (F6P) 和葡萄糖 6-磷酸 (G6P) 会略微降低 Rubisco 活性。 CO2 和 RuBP（在大气 O2 浓度下）的表观 Vmax 和 Km 的生化测量以及对接相互作用分析表明，CABP/CA1P 和 3-PGA 分别通过紧密和松散地结合到其催化位点（即与催化位点竞争）来抑制 Rubisco 活性。底物 RuBP)。 这些发现将有助于新策略的设计和生化建模，以改善 Rubisco 活性的调节并提高水稻碳同化的效率和可持续性。