Biologisches Institut II der Universität, Schänzlestrasse 1, D-7800, Freiburg i.Br., Germany.
Planta. 1990 Feb;180(3):429-34. doi: 10.1007/BF00198796.
The extent to which the appearances of nitrite reductase (NIR; EC 1.7.7.1) and glutamine synthetase (GS; EC 6.3.1.2) are coordinated was studied in mustard (Sinapis alba L.) seedlings. It was established by immunotitration that the increased activities of NIR and GS in the presence of light and nitrate can be attributed to the de-novo synthesis of enzyme protein. The bulk of the NIR and GS was found in the developing cotyledons. In the absence of nitrate in the growth medium there was no coordinate appearance of NIR and GS. While light strongly stimulated the appearance of GS, the level of NIR was hardly affected and remained low. On the other hand, in the presence of nitrate in the medium the appearances of NIR and GS were strictly coordinated, the GS level being considerably above that of NIR. It is argued that phytochrome-controlled synthesis of GS in the absence of nitrate is part of the mechanism to reassimilate ammonium liberated during proteolysis of storage protein and metabolism of the resulting amino acids, whereas the strictly coordinated synthesis in the presence of light and nitrate indicates the dominance of nitrate assimilation under these circumstances. The fact that the level of GS was always considerably above that of NIR appears to be a safety measure to prevent ammonium accumulation.
在芥菜（Sinapis alba L.）幼苗中研究了亚硝酸盐还原酶（NIR；EC 1.7.7.1）和谷氨酰胺合成酶（GS；EC 6.3.1.2）外观协调的程度。通过免疫滴定法确定，在光照和硝酸盐存在下 NIR 和 GS 活性的增加归因于酶蛋白的从头合成。大量的 NIR 和 GS 存在于正在发育的子叶中。在生长培养基中没有硝酸盐的情况下，NIR 和 GS 不会同时出现。虽然光照强烈刺激 GS 的出现，但 NIR 的水平几乎没有受到影响，仍然很低。另一方面，在培养基中有硝酸盐的情况下，NIR 和 GS 的出现是严格协调的，GS 的水平明显高于 NIR。有人认为，在没有硝酸盐的情况下，光敏色素控制的 GS 合成是重新同化在储存蛋白分解和由此产生的氨基酸代谢过程中释放的铵的机制的一部分，而在光照和硝酸盐存在下的严格协调合成表明在这些情况下硝酸盐同化占主导地位。GS 的水平始终明显高于 NIR 的事实似乎是一种防止铵积累的安全措施。
