Botanical Institute, University of Bonn, Kirschallee 1, 5300 Bonn 1, Federal Republic of Germany.
Plant Physiol. 1988 Nov;88(3):947-52. doi: 10.1104/pp.88.3.947.
The specific activities of nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase were determined in intact protoplasts and intact chloroplasts from Chlamydomonas reinhardtii. After correction for contamination, the data were used to calculate the portion of each enzyme in the algal chloroplast. The chloroplast of C. reinhardtii contained all enzyme activities for nitrogen assimilation, except nitrate reductase, which could not be detected in this organelle. Glutamate synthase (NADH- and ferredoxin-dependent) and glutamate dehydrogenase were located exclusively in the chloroplast, while for nitrite reductase and glutamine synthetase an extraplastidic activity of about 20 and 60%, respectively, was measured. Cells grown on ammonium, instead of nitrate as nitrogen source, had a higher total cellular activity of the NADH-dependent glutamate synthase (+95%) and glutamate dehydrogenase (+33%) but less activity of glutamine synthetase (-10%). No activity of nitrate reductase could be detected in ammonium-grown cells. The distribution of nitrogen-assimilating enzymes among the chloroplast and the rest of the cell did not differ significantly between nitrate-grown and ammonium-grown cells. Only the plastidic portion of the glutamine synthetase increased to about 80% in cells grown on ammonium (compared to about 40% in cells grown on nitrate).
我们测定了莱茵衣藻完整原生质体和完整叶绿体中的硝酸还原酶、亚硝酸还原酶、谷氨酰胺合成酶、谷氨酸合酶和谷氨酸脱氢酶的活性。经污染校正后，用这些数据来计算每种酶在藻类叶绿体中的部分。莱茵衣藻的叶绿体含有氮同化所需的所有酶活性，但除了不能在这个细胞器中检测到的硝酸还原酶。谷氨酸合酶（NADH 和铁氧还蛋白依赖性）和谷氨酸脱氢酶仅存在于叶绿体中，而亚硝酸还原酶和谷氨酰胺合成酶分别有大约 20%和 60%的质外体活性。与以硝酸盐作为氮源相比，用铵盐培养的细胞具有更高的 NADH 依赖性谷氨酸合酶（+95%）和谷氨酸脱氢酶（+33%）的总细胞活性，但谷氨酰胺合成酶的活性较低（-10%）。在铵盐培养的细胞中不能检测到硝酸还原酶的活性。氮同化酶在叶绿体和细胞其余部分之间的分布在以硝酸盐和铵盐培养的细胞之间没有显著差异。只有谷氨酰胺合成酶的质体部分在以铵盐培养的细胞中增加到约 80%（相比之下，以硝酸盐培养的细胞中约为 40%）。
