Martín-Figueroa E, Navarro F, Florencio F J
Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Centro de Investigaciones Científicas Isla de la Cartuja, Avda Américo Vespucio, s/n, 41092, Sevilla, Spain.
FEBS Lett. 2000 Jul 7;476(3):282-6. doi: 10.1016/s0014-5793(00)01722-1.
The gene encoding the ferredoxin-dependent glutamate synthase (Fd-GOGAT), glsF, from the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120, has been cloned and sequenced. Unlike other cyanobacteria, Anabaena 7120 contains only Fd-GOGAT, lacking NADH-GOGAT. The amount of glsF transcript and Fd-GOGAT activity were similar under all the nitrogen growth conditions tested. Enzyme activity, Western and Northern blot analyses indicated that Fd-GOGAT is absent in the heterocysts, while glutamine synthetase (GS) and NADP-isocitrate dehydrogenase (IDH) were present in these specialised cells. Our results clearly indicate that the GS-GOGAT pathway is not operative in the heterocysts, and hence glutamate must be imported from the adjacent vegetative cells, to sustain GS activity. Heterocysts probably export glutamine or another nitrogen rich compound like arginine to the vegetative cells.
已克隆并测序了来自异形胞形成蓝细菌鱼腥藻Anabaena sp. PCC 7120的编码铁氧化还原蛋白依赖性谷氨酸合酶（Fd-GOGAT）的基因glsF。与其他蓝细菌不同，鱼腥藻7120仅含有Fd-GOGAT，缺乏NADH-GOGAT。在所测试的所有氮生长条件下，glsF转录本的量和Fd-GOGAT活性相似。酶活性、蛋白质免疫印迹和Northern印迹分析表明，异形胞中不存在Fd-GOGAT，而谷氨酰胺合成酶（GS）和NADP-异柠檬酸脱氢酶（IDH）存在于这些特化细胞中。我们的结果清楚地表明，GS-GOGAT途径在异形胞中不起作用，因此谷氨酸必须从相邻的营养细胞中导入，以维持GS活性。异形胞可能会向营养细胞输出谷氨酰胺或另一种富含氮的化合物，如精氨酸。
