Hendrickson L, Sharwood R, Ludwig M, Whitney S M, Badger M R, von Caemmerer S
ARC Centre for Excellence in Plant Energy Biology, Research School of Biological Sciences, Australian National University, Canberra, ACT 2601, Australia.
J Exp Bot. 2008;59(7):1789-98. doi: 10.1093/jxb/erm373. Epub 2008 Mar 28.
The activation of Rubisco in vivo requires the presence of the regulatory protein Rubisco activase. This enzyme facilitates the release of sugar phosphate inhibitors from Rubisco catalytic sites thereby influencing carbamylation. T(1) progeny of transgenic Flaveria bidentis (a C(4) dicot) containing genetically reduced levels of Rubisco activase were used to explore the role of the enzyme in C(4) photosynthesis at high temperature. A range of T(1) progeny was screened at 25 degrees C and 40 degrees C for Rubisco activase content, photosynthetic rate, Rubisco carbamylation, and photosynthetic metabolite pools. The small isoform of F. bidentis activase was expressed and purified from E. coli and used to quantify leaf activase content. In wild-type F. bidentis, the activase monomer content was 10.6+/-0.8 micromol m(-2) (447+/-36 mg m(-2)) compared to a Rubisco site content of 14.2+/-0.8 micromol m(-2). CO(2) assimilation rates and Rubisco carbamylation declined at both 25 degrees C and 40 degrees C when the Rubisco activase content dropped below 3 mumol m(-2) (125 mg m(-2)), with the status of Rubisco carbamylation at an activase content greater than this threshold value being 44+/-5% at 40 degrees C compared to 81+/-2% at 25 degrees C. When the CO(2) assimilation rate was reduced, ribulose-1,5-bisphosphate and aspartate pools increased whereas 3-phosphoglycerate and phosphoenol pyruvate levels decreased, demonstrating an interconnectivity of the C(3) and C(4) metabolites pools. It is concluded that during short-term treatment at 40 degrees C, Rubisco activase content is not the only factor modulating Rubisco carbamylation during C(4) photosynthesis.
核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）在体内的激活需要调节蛋白Rubisco活化酶的存在。该酶促进磷酸糖抑制剂从Rubisco催化位点的释放，从而影响氨甲酰化作用。利用转基因双齿黄菊（一种C4双子叶植物）中Rubisco活化酶基因水平降低的T(1)代子代，来探究该酶在高温下C4光合作用中的作用。在25℃和40℃下，对一系列T(1)代子代进行筛选，检测其Rubisco活化酶含量、光合速率、Rubisco氨甲酰化作用以及光合代谢产物库。双齿黄菊活化酶的小异构体在大肠杆菌中表达并纯化，用于定量叶片活化酶含量。在野生型双齿黄菊中，活化酶单体含量为10.6±0.8 μmol m(-2)（447±36 mg m(-2)），而Rubisco位点含量为14.2±0.8 μmol m(-2)。当Rubisco活化酶含量降至3 μmol m(-2)（125 mg m(-2)）以下时，在25℃和40℃下二氧化碳同化率和Rubisco氨甲酰化作用均下降，当活化酶含量高于此阈值时，40℃下Rubisco氨甲酰化状态为44±5%，而25℃下为81±2%。当二氧化碳同化率降低时，1,5-二磷酸核酮糖和天冬氨酸库增加，而3-磷酸甘油酸和磷酸烯醇丙酮酸水平降低，这表明C3和C4代谢产物库之间存在相互联系。得出的结论是，在40℃短期处理期间，Rubisco活化酶含量不是C4光合作用过程中调节Rubisco氨甲酰化作用的唯一因素。
