FIXATION OF O-18(2) DURING PHOTO-RESPIRATION - KINETIC AND STEADY-STATE STUDIES OF PHOTORESPIRATORY CARBON OXIDATION CYCLE WITH INTACT LEAVES AND ISOLATED-CHLOROPLASTS OF C-3 PLANTS
FIXATION OF O-18(2) DURING PHOTO-RESPIRATION - KINETIC AND STEADY-STATE STUDIES OF PHOTORESPIRATORY CARBON OXIDATION CYCLE WITH INTACT LEAVES AND ISOLATED-CHLOROPLASTS OF C-3 PLANTS
复制标题
DOI：
10.1104/pp.62.6.954
复制
发表时间：
1978-01-01
期刊：
影响因子：
7.4
通讯作者：
LORIMER, GH
中科院分区：
文献类型：
--
作者：
BERRY, JA;OSMOND, CB;LORIMER, GH
质谱技术被用来跟踪掺入[18 O]氧的光呼吸途径的代谢产物。从C3植物菠菜（Spinacia oleracea L.）在CO2补偿点暴露于[18O]氧的滨藜和向日葵被18O大量标记。在每种情况下，只有1个羧基氧被标记。在乙醇酸盐的这种氧中的18O的丰度达到在仅5 - 10秒暴露于[18O]氧后提供的O2的丰度的50 - 70%。甘氨酸和丝氨酸分别在40和180秒后达到相同的最终富集。这证实甘氨酸和丝氨酸是由乙醇酸合成的。完整叶片中光呼吸中间产物的标记平均值达到饲喂中提供的β 2的59%。这表明，至少59%的乙醇酸光呼吸与分子O2的固定合成。由于光合作用O2在乙醇酸合成位点稀释了标记O2，因此该估计值肯定是保守的。乙醇酸合成的18O的产量进行了检查，在体外分离的完整的菠菜叶绿体在一个系统中，允许直接采样的同位素组成的O2在网站的合成。从这样的实验中的乙醇酸的同位素富集是90 - 95%的O2存在的孵育过程中。3-磷酸甘油酸酯的羧基氧也成为标记与[18O]在20和40分钟的饲料完整的叶片在CO2补偿点。对照实验表明，这种标记可能是由于在光呼吸过程中从乙醇酸直接合成3-磷酸甘油酸。3-磷酸甘油酸盐的平均富集为14 ± 10%。4%的甘氨酸或丝氨酸，其光呼吸途径的前体，在10个单独的喂养实验。可能这种恒定稀释的标签表明在CO2补偿点的光呼吸和光合作用源的3-磷酸甘油酸之间的恒定化学计量平衡。O2吸收足以占约一半的18O固定成甘氨酸在完整的叶片中的速率与完整的菠菜叶绿体观察。在CO2补偿点，完整叶片的氧吸收和生产表明每乙醇酸光呼吸约1.9个氧交换。分子O2到乙醇酸的固定加上乙醇酸到乙醛酸的过氧化物酶体氧化和甘氨酸到丝氨酸的线粒体转化可以占每个乙醇酸吸收高达1.75 O2。这些研究提供了新的证据，支持目前制定的光呼吸途径及其与光合代谢的关系。所描述的实验还提出了使用稳定同位素技术研究光呼吸速率以及体内光呼吸和光合作用之间的平衡的新方法。
Mass spectrometric techniques were used to trace the incorporation of [18O]oxygen into metabolites of the photorespiratory pathway. Glycolate, glycine and serine extracted from leaves of the C3 plants, Spinacia oleracea L., Atriplex hastata and Helianthus annuus which were exposed to [18O]oxygen at the CO2 compensation point were heavily labeled with 18O. In each case only 1 of the carboxyl oxygens was labeled. The abundance of 18O in this oxygen of glycolate reached 50-70% of that of the O2 provided after only 5-10 s exposure to [18O]oxygen. Glycine and serine attained the same final enrichment after 40 and 180 s, respectively. This confirms that glycine and serine are synthesized from glycolate. The labeling of photorespiratory intermediates in intact leaves reached a mean of 59% of that of the (2 provided in the feedings. This indicates that at least 59% of the glycolate photorespired is synthesized with the fixation of molecular O2. This estimate is certainly conservative owing to the dilution of labeled O2 at the site of glycolate synthesis by photosynthetic O2. The yield of 18O in glycolate synthesized was examined in vitro by isolated intact spinach chloroplasts in a system which permitted direct sampling of the isotopic composition of the O2 at the site of synthesis. The isotopic enrichment of glycolate from such experiments was 90-95% of that of the O2 present during the incubation. The carboxyl oxygens of 3-phosphoglycerate also became labeled with 18O in 20 and 40 min feedings with [18O] to intact leaves at the CO2 compensation point. Control experiments indicated that this label was probably due to direct synthesis of 3-phosphoglycerate from glycolate during photorespiration. The mean enrichment of 3-phosphoglycerate was 14 .+-. 4% of that of glycine or serine, its precursors of the photorespiratory pathway, in 10 separate feeding experiments. Possibly this constant dilution of label indicates a constant stoichiometric balance between photorespiratory and photosynthetic sources of 3-phosphoglycerate at the CO2 compensation point. O2 uptake sufficient to account for about half of the rate of 18O fixation into glycine in the intact leaves was observed with intact spinach chloroplasts. Oxygen uptake and production by intact leaves at the CO2 compensation point indicate about 1.9 oxygen exchanged per glycolate photorespired. The fixation of molecular O2 into glycolate plus the peroxisomal oxidation of glycolate to glyoxylate and the mitochondrial conversion of glycine to serine can account for up to 1.75 O2 taken up per glycolate. These studies provide new evidence which supports the current formulation of the pathway of photorespiration and its relation to photosynthetic metabolism. The experiments described also suggest new approaches using stable isotope techniques to study the rate of photorespiration and the balance between photorespiration and photosynthesis in vivo.