Eichelmann H, Laisk A
Tartu Ulikooli Molekulaar-ja Rakubioloogia Instituut, Riia tn 23, Tartu, 51010, Estonia.
Plant Physiol. 1999 Jan;119(1):179-90. doi: 10.1104/pp.119.1.179.
The content of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) (Et; EC 4.1.1.39) measured in different-aged leaves of sunflower (Helianthus annuus) and other plants grown under different light intensities, varied from 2 to 75 &mgr;mol active sites m-2. Mesophyll conductance (&mgr;) was measured under 1.5% O2, as well as postillumination CO2 uptake (assimilatory charge, a gas-exchange measure of the ribulose-1,5-bisphosphate pool). The dependence of &mgr; on Et saturated at Et = 30 &mgr;mol active sites m-2 and &mgr; = 11 mm s-1 in high-light-grown leaves. In low-light-grown leaves the dependence tended toward saturation at similar Et but reached a &mgr; of only 6 to 8 mm s-1. &mgr; was proportional to the assimilatory charge, with the proportionality constant (specific carboxylation efficiency) between 0.04 and 0.075 &mgr;M-1 s-1. Our data show that the saturation of the relationship between Et and &mgr; is caused by three limiting components: (a) the physical diffusion resistance (a minor limitation), (b) less than full activation of Rubisco (related to Rubisco activase and the slower diffusibility of Rubisco at high protein concentrations in the stroma), and (c) chloroplast metabolites, especially 3-phosphoglyceric acid and free inorganic phosphate, which control the reaction kinetics of ribulose-1,5-bisphosphate carboxylation by competitive binding to active sites.
在不同光照强度下生长的向日葵（Helianthus annuus）和其他植物的不同叶龄叶片中，所测得的1,5 - 二磷酸核酮糖羧化酶/加氧酶（Rubisco）（Et；EC 4.1.1.39）含量在2至75 μmol活性位点m⁻²之间变化。叶肉导度（μm）在1.5% O₂条件下进行测量，同时也测量了光照后CO₂吸收量（同化电荷，一种对1,5 - 二磷酸核酮糖库的气体交换测量指标）。在高光下生长的叶片中，μm对Et的依赖性在Et = 30 μmol活性位点m⁻²且μm = 11 mm s⁻¹时达到饱和。在低光下生长的叶片中，在相似的Et下依赖性趋于饱和，但μm仅达到6至8 mm s⁻¹。μm与同化电荷成正比，比例常数（比羧化效率）在0.04至0.075 μM⁻¹ s⁻¹之间。我们的数据表明，Et与μm之间关系达到饱和是由三个限制因素导致的：（a）物理扩散阻力（一个较小的限制因素），（b）Rubisco未完全激活（与Rubisco活化酶以及在基质中高蛋白浓度下Rubisco较慢的扩散性有关），以及（c）叶绿体代谢物，特别是3 - 磷酸甘油酸和游离无机磷酸，它们通过与活性位点竞争性结合来控制1,5 - 二磷酸核酮糖羧化的反应动力学。
